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Thread: popping through the exhaust at 4500 rpm or so.. HELP!

  1. #101
    Registered User madkaw's Avatar
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    I'm at a loss myself. You might wait till your wideband is hooked up at this point.
    I will be very interested in the outcome of this. I had a similar problem and it turned out to be those damn float bowl hoses. Looked great, felt great, but kinked up. Took a long time to identify the problem.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  2. #102
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    It seems I am right with the first two methods Blue.

    Nothing is really far from being 'spot on'. Everything appears to be as it should. I am going to blow out all the fuel lines and put everything back together. Then I will get some clear tubing and try to mark where the float comes up on the car. But all of this is just for ****s and giggles until I get my wideband installed this week! Should be here tomorrow or wednesday.
    1971 240Z HLS30-38691
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  3. #103
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    Just wanted to thank all of you again for the help. I am usually pretty savy with carbs. Was a bit of a Holley guru in my V8 days. and these SU's seem just wonderfully simple, but often the most complex things are the simplest. For the life of me, though, everything I do seems to result in ziltch. They are so clean you could eat off of them. This is truly a strange case.

    After I get the wideband stuff, it will at least point me in a direction...lean or rich.. well lets hope so.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
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  4. #104
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    Fuel filter? Finally got the car running great, but not sure if it is the same issue that Zedyone is dealing with. Changed out the fuel filter (I think that was the main issue), moved my 280ZX dizzy to 20 BTDC, Vacuum hose not attached, and drilled five 1” holes in the underside of my air cleaner housing (not sure if that was necessary but I had been wanting to do that). Seemed like it ran better with the air cleaner housing off. No popping at all now. It revs and runs nicely at over 6K rpm.
    Testing this can be dangerous. I am doing over 90MPH in 3rd gear at 5.5K. Fortunately traffic on freeway was light today. Doing around 60 MPH at 6.5k in second. Was not paying careful attention on one of these runs and locked up wheels when light turned red. No accident, but lots of smoking rubber. No ABS on this vehicle. Anyway, glad to be back to normal.
    On a side note, I do have to say, I rarely take my car over 4K RPM. My typical shift point is 3K. Nice to know that it will do it, but can’t say it is very useful

    Rich

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    Registered User 5thhorsemann's Avatar
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    Quote Originally Posted by motorman7 View Post
    On a side note, I do have to say, I rarely take my car over 4K RPM. My typical shift point is 3K. Nice to know that it will do it, but can’t say it is very useful

    Rich
    It will be very usefull when you need it. Kind of like my H&K USP .45 ACP, I haven't ever had to use it, but it sure feels good knowing it's there if I ever need it.

  6. #106
    Supporting Member Zedyone_kenobi's Avatar
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    H&K,

    Very nice...
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  7. #107
    Supporting Member Zedyone_kenobi's Avatar
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    UPDATE:


    5pm this evening I get all the carbs back together and fill them with a lighter oil. I used Marvel Mystery oil per somebodies suggestion. Car now pops and sputters at any throttle change above 2200 rpm. It is leaning out way to fast as that piston rises so much faster. Definitely a step in the wrong direction!

    I will clean out the carbs again and fill them with straight 20 wt oil. I have no idea what the SU oil is that I bought. I only know the marvel mystery oil made the plunger FAR easier to push up.
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
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  8. #108
    Registered User madkaw's Avatar
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    Trans fluid works also.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

  9. #109
    Registered User 30 Ounce's Avatar
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    Don't jump directly to 20wt, try 5wt fork oil or ATF (they are about the same), then 10wt then 15wt. There is a huge difference between each one. SU oil is about 12.5wt.
    74 260Z late
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    I'm running 10W30

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    For what it's worth I found that both 10W30 and 20wt worked well in my SU's.
    Steve

    1973 240Z (daily driver)
    1971 240Z (track car)

  12. #112
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    Try a slow acceleration from 1000rpm on a flat stretch in 1st then 2nd then 3rd gear to see exactly where the popping occurs.

    The damping oil should only affect:

    1. throttle transitions due to pedal
    2. engine vibration/road bumps
    3. engine rpm changes from gear changes

    If you do the test above you will rule out the oil viscosity.
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  13. #113
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    Good ideas guys.

    Blue, the reason I am on the oil right now is I sort of half way ran that test yesterday with the Marvel Mystery oil (about 3 wt according to interwebz sources) and any gradual roll on to the throttle seemed okay, but any drastic change at all the engine just about stopped running. THe more I moved the butterflies the more drastic it became.

    So here is my logic. Flawed as it may be.

    Right now my pistons drop perfectly in tune with each other. With or without the top of the carb screwed in. So I know there is no hang up in the needle or the piston. CHECK!

    With SU oil (12.5 wt, thanks 30 Ounce), it popped and sputtered at about 4500 rpm
    With Marvel Mystery oil (3 wt ), it popped far worse at about 2500 rpm
    I am now running straight 20 wt. We will see when I get her on the road today, if the trend continues, this SHOULD get me on the right track...

    But I will not rule out a 15wt oil if this works as well.

    Like a bad sit com... The saga continues...
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
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  14. #114
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    Quote Originally Posted by Zedyone_kenobi View Post
    I did notice that when I first looked at the front float, that the wrist pin was dislodged on one side. Now I do not know if I did that when I removed it or not, but it was the only thing noteworthy at all in inspecting the floats.
    The bowl and lid were designed such that they cannot be assembled properly if the pin is out of place. If the pin were so badly out of place that it had slipped completely out of one hole, then the pin would hit the bowl during assembly and you wouldn't be able to get the lid on flush.

    As for damper oil... The 72 manual suggests 10w-30 and the 74 manual suggests 20 weight or 10W-30.

    Like a bad sit com... The saga continues...
    No kidding!

    I know I'm reaching, but I wonder if there's something wrong with the PCV system somehow. The PCV is supposed to allow a pre-determined "unfueled" amount of air around the carbs, but it takes manifold vacuum in order to make that happen. Because of the way the PCV is designed, if there's not enough vacuum (like maybe when you are at part throttle), the PCV will pass too much air.

    Maybe you could cap of the PCV for a test run just to see what happens? Capping it will richen your idle mixture, but once you get off idle the change should be small enough that it won't matter much.

  15. #115
    Supporting Member Zedyone_kenobi's Avatar
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    I will put that on the list after I try this 20 wt.

    I wonder what the 71 manual says to put in it. I cannot imagine it would be anything different. I have been running the SU oil for a while now as MSA says ..."this is the perfect oil for your SU's".... If it is 12 wt, I cannot imagine why they said that. When I first got my SU's from Z therapy, I put 20wt in them and that was as good as they ever ran. Then I remember switching to the MSA SU oil because... well because it was SU oil! I somehow thought it would work better...
    1971 240Z HLS30-38691
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  16. #116
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    Yeah, I'm with you. I would expect that "SU oil" would be perfect for the SU's!!

    I haven't downloaded all the different years of FSM's. I got 72, 73, and 74, so I don't know what 71 calls for.

    Another straw... I just noticed in your sig that you've done some changes to your evap system? What can you tell us about that? I can imagine scenarios where the evap system could allow too much air under certain conditions but still appear to be working correctly at idle.

  17. #117
    Supporting Member Zedyone_kenobi's Avatar
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    I made my evap system back to 100% stock. All hoses that are suppose to run to the tank, run to the tank. All hoses that are suppose to run to the engine and filler neck, run to the engine and filler neck.
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  18. #118
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    FSM states #20 weight Mobil oil. It says not to uses #30 weight or higher.

    I will add that the float dimensions worked for my carbs, but I did wind up richening the float setting for max power. What I am saying is that the engine would rev up, but there wasn't much power at the upper end. You still may need to adjust them in the end. Good to see your making chances that actually effect the engine.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Thanks for your advice madkaw! I certainly appreciate it.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Quote Originally Posted by madkaw View Post
    FSM states #20 weight Mobil oil. It says not to uses #30 weight or higher.
    72 FSM (EF-26) says to use 10W-30, but not SAE 30. They must have expected that SAE 30 would be too thick when cold, but the multigrade would be suitable.

    As for the evap system, I just refreshed my memory on the early (flow guide style) systems and after further review, my mistake... I cannot come up with any reasonable explanations how the (early) evap system could cause any extra air around the carbs into the engine. Later carbon canister style, yes. But the flow guide style like what you have? No.

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    Having read most, if not all of this thread's posts, I notice a similarity of sorts with what I experience with my Mikuni set-up. But only when everything is sorta cold. Once the engine and carbs are fully heat saturated, the stumbling goes away... I'm sure that's NOT the issue you have, Stephen, so take it as what it is....
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    Supporting Member Diseazd's Avatar
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    Zedy.....I'm coming in late on this thread so I hope this hasn't already been checked. Most popping through the exhaust in my experience has been caused by air being drawn into the intake or exhaust manifold. My green car had a popping because I had replaced the 3 studs in the downpipe with the wrong studs (from the head instead of the right ones ). They bottomed out before sealing the little downpipe gasket tightly. Took forever to find that one, but completely quiet now. Also, headers are notorious for poor matching of the flat area that snugs up to the intake/exhaust gasket. An intake or exhaust gasket leak will cause a popping......oxygen burns! I would start by checking your downpipe gasket (make sure it seals), followed by pulling the intake manifold and exhaust header and checking the intake/exhaust manifold for leaks (replace the gasket). All IMO......Good Luck Guy
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  23. #123
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    Thanks very much Guy.

    UPDATE:

    I am about ready to throw these freaking SU's in the river. After I shoot them.

    THe 20wt oil did absolutely nothing to the problem.

    If I gradually push the throttle about an inch, the car pops loudly through the exhaust. If I floor it it will pull hard through all 3 first gears.

    Guy, I have a thought that you may be on to something. There is just no reason these SU's should not work the way they are...

    What the hell would cause popping and a complete loss of acceleration at part throttle but works when at wide open throttle.

    I am going to put the SM needles back in and call it quits until I get my wideband.

    I have had it.. screw these. Maybe I need a time out.

    spending 1499 dollars on webers or 1650 on mikunis is sounding like a far better option at this point!

    HAHA
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  24. #124
    Supporting Member Zedyone_kenobi's Avatar
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    Guy, I will check out my exhaust tonight to be sure.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    http://www.classiczcars.com/forums/s...ngs&highlight=

    Zedy.....You can check for vacuum leaks (which would cause your problem) with the info that BLUE provided. I would just pull the exhaust and intake manifolds off and install new gaskets. It's a 1 1/2 hour job.
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  26. #126
    Supporting Member Zedyone_kenobi's Avatar
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    I have not checked for vacuum leaks around the exhaust guy. I did check for manifold bolt tightness, and all the nuts on the studs were as I left them. All the carbs are tight. I will run an extensive battery of vacuum checks when I get home with my vac gage. That is easy enough. I did that earlier, and I think I got around 20 " if I recall. I wrote it down in my Z car journal.

    Still it cannot hurt to check.
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  27. #127
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    I can understand the exhaust causing the popping, but not the loss of acceleration at part throttle. That would be a huge leak that he would hear. Vacuum leak is a possibility but his idle is great?

    Is the power there at WOT?
    Do you think your engine is making it's normal power when revving out or is it just running up the rpms with less power?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Man, that is tough, I have no idea, it seems to pull okay, but I have only ever driven one other classic Z and it was stock. I would say it feels like a stock Z madkaw. It revs pretty nicely at WOT. Of course, the tach go bazerk when I get close to 6000 rpm
    1971 240Z HLS30-38691
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    Vacuum leaks is my next check. It just makes sense. I think it is safe to say we have ruled out SU oil as a cause. It popped with

    2 wt
    12.5 wt
    20 wt

    It popped with SM needles and stock OEM needles
    Pistons are moving up and down in the domes at the same speed.

    Car has a great idle.
    Car ran noticeably better with SM needles


    Here is what I have NOT done:
    I have checked fuel pressure from my brand new fuel pump, which was good, but I have not checked volume. OR pressure while the car is being driven. But I ruled that out as if I can rev to 6500 rpm at wide open throttle I am getting fuel.

    I have NOT checked if the fuel level is right at the top of the jet opening in the carb body, I just assumed the float bowls being properly adjusted was okay.

    I have not done a proper vacuum check of my power brake line for leaks (will do that today)

    I have not checked for a lose connection of my header to my exhaust pipe, but have checked most of the bolts on my header to my cylinder head, but not all.

    I have not installed a wideband O2 sensor yet, but it will be here tomorrow which should GREATLY help narrow down things in a direction of goodness.
    1971 240Z HLS30-38691
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  30. #130
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    again, webers or mikunis

    haha
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    After experiencing what sounds like the exact same popping issue, as I noted earlier, I can say that I did very little adjusting to my SU’s to fix the issue, other than minor mixture adjustment. I even had the popping at idle at one point and then again at 3K. My SU mixture nuts are now at about 1.5 turns. I could adjust these either way turn and not make much difference in the way it is now running, which is just about perfect. I think the fuel delivery/fuel filter was the issue. I thought what I had installed originally was pretty new and clean, but apparently it was not. I installed the new filter (made in China) and did the 20 degree advance on the timing and that seemed to do the job.

    As I mentioned before I also punched some holes in the air cleaner housing. Not sure if this was a contributor; the car just seemed to pop at higher RPM’s when I tested with the air cleaner off (when I was having the popping issue). Another problem I had with the air cleaner housing (a couple months earlier) was I had somehow accidentally flipped the cold/hot baffle on the front of the housing to “cold” (I live in SoCal so never need this setting). Anyway, the Z was really dogging and popping at about 3.5-4K in this condition. Flipped this back over to hot and made a big difference. Anyway, Just thought I’d pass this on. Definitely a very frustrating issue.

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  32. #132
    Registered User madkaw's Avatar
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    I'm still stuck on float adjustment.
    The jet needles are being set flush against the piston with the jet collar flush??
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    I have 2 extra fuel filters lying around. I will put one on when I get home today before I check out my car for vacuum leaks. Cant hurt.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Quote Originally Posted by Zedyone_kenobi View Post
    I have 2 extra fuel filters lying around. I will put one on when I get home today before I check out my car for vacuum leaks. Cant hurt.
    Yes, I was surprised because my fuel filter (made in Israel) was pretty new. May have been some remnants of debris from the earlier fuel tank mess. I also got a new fuel pump several months ago, but that made no difference when swapped out with my old one. May put the old one back in as it is the original Nippondenso (?) pump. The new one is that cheapo stamped sheet metal type. (Looks like the old one would pump more fuel as the diaphragm diameter is larger. Of course the lever arm fulcrum would need to be compared to verify). I thought this may have been part of my earlier popping problem, but I never did switch back to the old one. May do this when I get some time. You may also want to try the timing advance and a run or two without the air cleaner to see if that makes a difference. For me, with the ZX dizzy ‘over-advanced’, I get a bit of ping at the lower RPM, but the car is VERY happy at 3K. Car pulls very nicely from 3K-6K now. And, no popping at all.

    Best regards,
    Rich

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    WOW, a 20 degree timing advance- that would make a difference on any set up. That's like being a tooth off!!



    Quote Originally Posted by motorman7 View Post
    After experiencing what sounds like the exact same popping issue, as I noted earlier, I can say that I did very little adjusting to my SU’s to fix the issue, other than minor mixture adjustment. I even had the popping at idle at one point and then again at 3K. My SU mixture nuts are now at about 1.5 turns. I could adjust these either way turn and not make much difference in the way it is now running, which is just about perfect. I think the fuel delivery/fuel filter was the issue. I thought what I had installed originally was pretty new and clean, but apparently it was not. I installed the new filter (made in China) and did the 20 degree advance on the timing and that seemed to do the job.

    As I mentioned before I also punched some holes in the air cleaner housing. Not sure if this was a contributor; the car just seemed to pop at higher RPM’s when I tested with the air cleaner off (when I was having the popping issue). Another problem I had with the air cleaner housing (a couple months earlier) was I had somehow accidentally flipped the cold/hot baffle on the front of the housing to “cold” (I live in SoCal so never need this setting). Anyway, the Z was really dogging and popping at about 3.5-4K in this condition. Flipped this back over to hot and made a big difference. Anyway, Just thought I’d pass this on. Definitely a very frustrating issue.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    I currently run 17 degrees BTDC per the european spec dizzy I had mine recurved to match.

    I do not run a Vacuum Advance. I have made the runs with the BARE SU;s with no air cleaner (just plain easier to adjust quickly), with the air cleaner base on but no filter or housing (to get the benefit of the air horns), and with the air cleaner.

    NO noticeable difference either way. Get popping from the exhaust in all part throttle situations near 4000 rpm.

    I just do not see it being a fuel delivery problem when I will run at WOT, but not part throttle
    1971 240Z HLS30-38691
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    ZCCIV Webmaster motorman7's Avatar
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    Quote Originally Posted by madkaw View Post
    WOW, a 20 degree timing advance- that would make a difference on any set up. That's like being a tooth off!!
    No Vacuum advance. Very similar to Zedyone, with just 3 degrees difference. Manual says 17 for non-smog equipped cars, so not too far off.

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    Quote Originally Posted by madkaw View Post
    I'm still stuck on float adjustment.
    The jet needles are being set flush against the piston with the jet collar flush??
    With the float hung upside down, I picked up the float and the instant it touched the needle with the tang, I took the measurement. It was about .55" as per the factory manual. This differs from the SU video as he showed the float top parallel with the float bowl cover when held upside down. Maybe I should ask Bruce for an explanation of this.
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    Registered User doradox's Avatar
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    Quote Originally Posted by Zedyone_kenobi View Post
    Ah, I never really looked that hard into that. Yup, That goes to my crank case ventilation, check, PCV valve is new when I got the carbs.
    I removed it and it rattles when I shake it...

    I will check to see if there are some diagnostic checks I can do on it.
    Did you ever check this? The PCV valve could be causing you to go lean at tip in if the spring is defective. Simply pull off the hose, cap the valve, and go for a drive.

    Also, have you tried running at 3, 3.5, 4 turns out on the mixture? If you are lean this should make an improvement. If it does then you can continue on your quest to find out why you are lean.

    Steve

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    I cannot go more than 3 turns out as the car will not run anymore. It stumbles so badly it barely runs...

    I took off the PCV and blew into it from both sides... only could blow through it in one direction

    I will cap it though and go for a drive..
    1971 240Z HLS30-38691
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    Boat Anchor Repairman Captain Obvious's Avatar
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    Quote Originally Posted by Zedyone_kenobi View Post
    I cannot go more than 3 turns out as the car will not run anymore. It stumbles so badly it barely runs...

    I took off the PCV and blew into it from both sides... only could blow through it in one direction

    I will cap it though and go for a drive..
    Yeah, the PCV "rattle" and blow through tests only goes so far. Capping it and going for a drive would be a better test.

    What happens when you go more than 3 turns out on the nozzle? It goes so rich that the car won't run at all?

    I'm with you on the exhaust leak and fuel delivery stuff. If you are OK at full throttle, then it's not fuel delivery, and anything downstream of the exhaust valve (like a headpipe leak) isn't going to give you any significant performance impact. Popping noise maybe, but no performance changes.

    So. Let me jump ahead a little just for cuiosity... So you put the wideband on and it shows you are very lean at midrange. What are you going to do then?

    And conversely, if the wideband shows you are very rich at midrange. What then?

    What's "the plan" in either event?

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    I would be happy to swap my SU's with yours for trouble shooting purposes. Just as we did with the distributors. A couple of gaskets and an afternoon and we'll know if the carbs are to blame.
    Steve

    1973 240Z (daily driver)
    1971 240Z (track car)

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    I'd bet the wideband will show a lean condition when the engine is popping. A missfire will almost always show as lean as unburnt fuel and extra air gets to the sensor. The interesting data will come just before 4500rpm and just after.
    Steve

    1973 240Z (daily driver)
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    I have spent some time thinking of this actually Captain.

    The answer varies so wildly with the results. I do not forsee the wideband being so cut and dry. I hope it does, but in reality we both know that it will be XXX at idle, and YYYY at 2500 rpm, then ZZZZ when it is popping. I am hoping to see a trend.

    If I know I am leaning out, then I can try to find out where in the fuel delivery I am leaning out. Is my fuel pump providing enough fuel, is the float level adjustment right. Is unmetered air entering into the system.

    If I know I am rich, then the list gets easier. Try to find out where the extra fuel is coming from.

    the thing is, all it does is put me into the right ballpark, and gives another data point to help diverge ideas from one another. It also is a quantifiable piece of data which directly relates to the engines running.

    My thought is that I should not be running rich here and lean there too much. My car is stock except for the header and the custom curved dizzy. Head, cam, block, etc is all stock. Stock SU's should be able to compensate for any small variances between my setup and a totally stock setup. Perhaps my engine is not totally healthy, although that would surprise me. Maybe my cam is not totally up to snuff, but that would surprise me as well.

    Your question is one of great importance...and one I shall have to deal with eventually.
    1971 240Z HLS30-38691
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    That is VERY generous of you Steve!

    But I cannot do that to your daily driver. I would never ask you to. Not yet anyway ! HA HA.

    I would rather just buy the mikunis and webers and have those as a back up to my SU's, or have my SU's as a back up to the triples.

    I wish I had an easy answer to what this was. We have picked the low hanging fruit. Now it is time to find the more obscure things that have a drastic effect. Things like the vacuum leak come to mind.

    When I go more than 3 turns out the car just stumbles and dies when it tries to idle. Perhaps I should try to open up the flappers a bit more to keep her running. A wideband will tell me how lean or rich I am at idle so that should provide some insight to that issue.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
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    I changed out my fuel filter same thing happens. Nothing of note. Should also note my last chance filters in the SU's were very clean as well when I looked at the float bowls

    I put a vacuum gage on the manifold vacuum going to the power brakes. After the engine is warmed up, it pulls 19-20 psi pretty steady at 750 rpm.


    NOTE:
    I checked out my exhaust slip flanges from where my 6-2-1 header goes from 6 to 2. They were a few turns loose each. The one that goes from 2 to 1 I could not get to without jacking up the car.
    Last edited by Zedyone_kenobi; 01-04-2012 at 02:19 PM.
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    Could the popping be "knock" and you are advancing too quickly?
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    Nah, when steve91tt we ran the car at essentially 1 deg BTDC with his distributor and it still did it.

    It popped when I ran it at 10 deg, 14, deg and 17 degrees, and it fully advanced by 3100 rpm or so.


    I got my Innovative LC-1 wideband in today. I just need to wire it up and get my exhuast drilled for the metal cupling. I was hoping it would have come with a plug AND a sensor. But it only came with a sensor. I wanted to get it installed with the cap on, then come home and install the sensor. Now I will have to do it a bit backwards.

    Wire the computer up and install the gage, and then drive to a muffler shop to get the bung welded on and a hold drilled.
    Last edited by Zedyone_kenobi; 01-04-2012 at 04:40 PM.
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    Registered User doradox's Avatar
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    Quote Originally Posted by Zedyone_kenobi View Post
    We have picked the low hanging fruit.
    Speaking of that, have you plugged the PCV or tried pulling the choke to artificially enrich the mixture as several others have suggested?

    Steve

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    Popping through the exhaust is usually rich and popping through the intake is usually lean (or very bad spark scatter or improper timing or plug wire mix up).
    There is scarcely anything in the world that some man cannot make a little worse, and sell a little more cheaply.
    The person who buys on price alone is this man's lawful prey.


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    I do not have a suitable plug for the PVC yet but plan to pick one up tomorrow along with a plug for my o2 sensor bung. I will try the choke tomorrow but I recollect doing that before with little success but let me confirm for you. No stone left unturned!

    Have I mentioned you guys rock

    Getting my o2 sensor hooked up must become top priority. It will remove some of the guessing
    1971 240Z HLS30-38691
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    Quote Originally Posted by Blue View Post
    Popping through the exhaust is usually rich and popping through the intake is usually lean (or very bad spark scatter or improper timing or plug wire mix up).
    Which is why it runs better with SM needles? And has no other symptoms of being too rich? If it's mixture related yanking the choke will either make it worse or better. I imagine that information would be useful. I can't imagine a single good reason why one wouldn't try it. As a matter of fact I can't imagine a single good reason why it wouldn't be the first thing you would try.

    Steve

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    I'm having a little trouble justifying a typical vacuum leak. You said your idle is perfect, and I would expect the impact of your typical "constant" vacuum leak to decrease as you give it pedal. That's why I was trying to think of more atypical vacuum leak sources that might get worse off idle.

    Well whatever you find, I'm pullin' for ya!!

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    You need to get this off your list. A wrong setting would be most apparent at higher rpm cruise. If anything I would go rich on the setting-the worse scenerio would be a bit of fuel in the carbs. To low of a level will throw off your mixture at higher load/higher vacuum scenerios. I don't believe adjusting the mixture screws will make up for a poor setting on the floats. I know you have the factory setting in there, but tweeking the floats a couple off MM's will not hurt.
    What I have witnessed is a car that I rebuilt the carbs on that it would run in all parameters, but not much power top end. It was all about the floats not being set right. Believe it or not I just tweeked the floats without a real measurement-just richened it up a bit. Car made much more power and never overflowed the bowls.



    Here is what I have NOT done:
    I have Herchecked fuel pressure from my brand new fuel pump, which was good, but I have not checked volume. OR pressure while the car is being driven. But I ruled that out as if I can rev to 6500 rpm at wide open throttle I am getting fuel.

    I have NOT checked if the fuel level is right at the top of the jet opening in the carb body, I just assumed the float bowls being properly adjusted was okay.
    Last edited by madkaw; 01-05-2012 at 03:36 AM.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    Quote Originally Posted by Zedyone_kenobi View Post
    UPDATE:


    5pm this evening I get all the carbs back together and fill them with a lighter oil. I used Marvel Mystery oil per somebodies suggestion. Car now pops and sputters at any throttle change above 2200 rpm. It is leaning out way to fast as that piston rises so much faster. Definitely a step in the wrong direction!

    I will clean out the carbs again and fill them with straight 20 wt oil. I have no idea what the SU oil is that I bought. I only know the marvel mystery oil made the plunger FAR easier to push up.
    Did you ever try this with 30 wt recommended by the FSM? Or maybe some 40 or 50 to bracket the results?

    Steve

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    Nope, but I intend to.

    I will get a bottle of SAE straight 30 wt to give it a try.

    I am sort of on hold until after I get my O2 sensor in. My time is very limited each day, and I try to squeeze as many ideas you guys give me as I can. But windows are small.


    I will make every effort to go for a drive to day to try the choke thing again. I just do not remember the results.

    I will also try today to block off the PCV and see what happens. I am going to order more SU float bowl gaskets and try to get an actual visual reading on that float level with a straight edge and a piece of clear tubing. While I do that I am going to put the SM needles back in.

    You guys are worth your weight in SU oil let me tell you!
    1971 240Z HLS30-38691
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    I know it's tough, but hang in there. These are the situations that force me to study and research and relearn the basics. You will be the first to pop in when someone starts a thread on SU problems. !!!

    Google SU carbs and their operation and critical float adjustment. The more I learn about carbs and fuel injection, the more I realize how good and easy FI is
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
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    This is how I set my float levels and it worked great.

    SETTING SU FLOAT BOWL LEVELS
    We've all spent afternoons syncing the carb airflow, topping up the damper oil and making sure the jet needle/fuel nozzle levels are set properly (2 1/2 turns down, etc). But how many of us have checked to make sure the gas float levels are identical on each carb? This is actually a very big deal. If the fuel levels are different in each float bowl, even a small bit, one carb will always be lean or rich compared to the other.

    The issue is that the SU uses a combination of incoming gas and the float closing the fuel-valve to create a steady fuel level at the tip of each fuel nozzle. If this fuel level varies between carbs then its also at a different level on each jet needle.



    HOW TO MEASURE FUEL LEVELS?
    This has been covered in several places online. Be careful since you're dealing with gasoline(!) Mark the front of the float bowl 23mm down from the top edge of the bowl (not the top of the lid). These measurements are done with the carbs on the car.

    - Get some small diameter clear plastic hose from the hardware store, cut a piece about 18" long.
    - Connect one end to a float bowl's outlet and run the other end up over the carb. Some people connect the hose to the drain plug on the float bowl but the fuel hose outlet is a lot easier.
    - Bring your fuel pressure to what it would be while idling. This means if you have a mechanical fuel pump turn the engine over a few times with the coil wire off. With an electric fuel pump just turn the ignition on to pump up the fuel pressure.
    - The fuel level will equalize in the hose and should line up with the 23mm mark on the float bowl. By sighting the level in the hose and bending the tab on each float you can get the float fuel levels to match within a millimeter.

    HOWEVER: Even though adjusting the floatbowl levels to 23mm down is a factory setting, it doesn't guarantee that the fuel levels in the carbs are the same.

    THE TRICK:
    I did some measuring with a straightedge and found that on my 4-screw SUs a 23mm fuel level in the float bowl corresponds to exactly 1 centimeter (10 millimeters) below the fuel nozzle "ledge" in the carb. But how do you see to measure fuel 1 centimeter down inside the fuel ozzle? See below.

    - Remove the dome and main piston from each carb so you can look down the tip of both fuel nozzles.
    - Screw each mixture nut exactly 10 turns down from fully up. Each full turn drops the nozzle tip 1 mm, so 10 turns puts the tip of the fuel nozzle 10 mm (1cm) down....which happens to be the 23mm float bowl level.
    - Then look down the tip of each fuel nozzle and adjust each float to set the gas level at the fuel nozzle tip.

    I ended up taking mine to 9 turns down and set the fuel at the meniscus of the tip. Then when I went to 10 turns the fuel was exactly at the tip. A bit of a juggling act but after a few minutes you will get the hang of it. When you get them to match it's a great feeling.

    NOTE #1: if your mixture nut won't go down more than a few turns, it's because the factory "stopper" next to the nut is still in place. Unless originality is a concern, you can permenantly remove both stoppers from the bottom of the carb.

    NOTE#2: if the fuel level is too high and overflows the nozzle tip, you will need to drain each float bowl a bit before starting again.

    The result was a lower, more solid idle and less choke needed at startup. I get no stumbling off idle and part-throttle acceleration is smoother, acceleration more powerful. Cruising on the interstate requires a lighter touch on the accelerator. Interesting.
    74 260Z late
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    Supporting Member Diseazd's Avatar
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    Quote Originally Posted by Captain Obvious View Post
    I'm having a little trouble justifying a typical vacuum leak. You said your idle is perfect, and I would expect the impact of your typical "constant" vacuum leak to decrease as you give it pedal. That's why I was trying to think of more atypical vacuum leak sources that might get worse off idle.

    Well whatever you find, I'm pullin' for ya!!
    Could it be a leak on the other side of the throttle plate (maybe shot throttle shaft bushings)? Zedy....If I were you, I think I would accept Steve's (tt) generous offer to try his SU's. This would eliminate the carbs as a source of your problem. It's only a 30 minute swap. Why not?
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    This is something I think I need to do. How many times can I reuse the stock cork SU fuel bowl gaskets?

    I was going to try the clear fuel hose trick this evening if I could. I probably will not be able to get the O2 sensor installed for a week. Just too busy.

    I have not verified my fuel level in my float bowls, but by God I will soon!
    1971 240Z HLS30-38691
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    Now with 100% more DATSUN SPIRIT L28 Power
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    Quote Originally Posted by Diseazd View Post
    Could it be a leak on the other side of the throttle plate (maybe shot throttle shaft bushings)? Zedy....If I were you, I think I would accept Steve's (tt) generous offer to try his SU's. This would eliminate the carbs as a source of your problem. It's only a 30 minute swap. Why not?

    I just feel bad about asking him to take his carbs off his daily driver. I know it is just 8 bolts, but still. I will do that before I do anything drastic I promise.

    first I need to get my fuel level in my carbs verified beyond a shadow of a doubt. As far as air leaking on the throttle shaft, I have to believe that Ztherapy carbs with their patented seals and bearings have eliminated this as a possibility... But a carb swap would be an easy way to verify this...
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
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    first I need to get my fuel level in my carbs verified beyond a shadow of a doubt. As far as air leaking on the throttle shaft, I have to believe that Ztherapy carbs with their patented seals and bearings have eliminated this as a possibility... But a carb swap would be an easy way to verify this...[/QUOTE]
    I agree....and I would assume the floats were set correctly also.
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    Supporting Member Zedyone_kenobi's Avatar
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    Maybe I should get data and not assume anything...

    At NASA here in the cryogenic propulsion division, we have a saying...

    'In God we trust, all others bring data....'
    1971 240Z HLS30-38691
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    reuse the gaskets until they fall apart--basically. If your careful you can take the covers off many times without issue.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Cork float bowl gaskets on the other hand are generally not reusable. I've made my own in the past out of gasket paper. The home made ones are good for several uses.
    Steve

    1973 240Z (daily driver)
    1971 240Z (track car)

  66. #166
    Supporting Member Zedyone_kenobi's Avatar
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    Going to check out the float levels tomorrow when I hopefully get my O2 sensor bung welded in!
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    I managed to get outside and check the float bowl levels using the clear hose trick mentioned by the wonderful folks of this board. I marked the outside of the fuel bowl .906" down from the fuel bowl rim (I know technically it is supposed to be measured from the inside lid, but it is close enough to see if I was off.

    The front bowl was just about right up to that mark I made, not quite but close. The rear bowl was about a 1/4 to a half inch below that mark. I cranked the car for a good 8 seconds each time to give the bowls plenty of time to fill up.

    So I removed the rear bowl and bent the little tang the slightest bit toward the float. I reinstalled it and presto, dead even with the line.

    I have not had a chance to drive it yet, as tonight is date night with Mrs. Zedyone, but tomorrow morning, I will take that baby for a spin. I cannot find a shop to weld in my O2 sensor on a saturday, so I am stuck waiting a bit longer to get that working. But I will report back after my drive!
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  68. #168
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    A quarter inch out of spec might be enough to be noticeable, but what could a low bowl level do to mid-RPM cruise that wouldn't be worse at high RPM WOT?

    Hey, I forgot to ask you the other day... When you bought OEM stock needles, what needle number did you buy? Do the new needles even have numbers marked on them? My round tops have N-27's but I believe they ran a couple different numbers over the first few years.

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    They have no numbers on them, I looked. But the invoice from Z therapy said N27 I am 99% sure. I will check for you and get back.

    I agree about the low float bowl having little to do with part throttle popping, but I have to check everything at this point...

    I will figure this out if I have to replace every single part on this car one at a time. If that means building up an entirely new L24 so be it, but as GOD as my witness I will track this down!
    Last edited by Zedyone_kenobi; 01-07-2012 at 05:07 AM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Yeah, I understand completely. I don't fault you one bit for trying the seemingly unrelated. I'd be trying anything by now as well.

    Something else I forgot to ask a while ago... I wanted to confirm the circumstances of the mid-RPM misfire. Does it occur only under light load (like when you are cruising along at a steady speed at 4500 RPM-ish) or does it occur under no load just sitting still with your foot a little bit on the gas pedal? (Or both?)

    Thanks for the needle info. I've been messing around with my flat-tops and have measured a few different needles recently including the N-27. I should probably post my findings sometime.

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    Supporting Member Zedyone_kenobi's Avatar
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    Only occurs when I am actually driving, sitting still and revving it is perfect
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    I don't think it is carbs.


    I think it is related to any of these

    -slop in the drive spindle to distributor
    - slop at crank gear to distributor drive spindle
    - mechanical timing not correct by PO (crank timing chain and cam)

    I re-read your early posts and this stuck with me:

    "Seems I have had this issue since I owned the car in some form of severity or another. When I first bought the car, it would simply NOT rev past 4500 rpm at all. Now I can get it to rev to 6500 rpm thanks to the Z therapy carbs, but now it is popping pretty bad on the top end. "


    Looks like the ZT carbs may have masked a deeper issue.
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    I'm starting to think along the same lines as Blue. I think it's time to open the valve cover and check timing marks to confirm valve timing.

    To check for slop in the distributor drive system you can use a timing light to see if the timing jumps around or stays nice and constant at various RPM's In other words, check for nice solid timing at 1000, 2000, 3000, 4000 and 5000. If you see the timing mark jumping around then there is slop in the system. It should be very steady and consistent.
    Steve

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    1971 240Z (track car)

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    So did I miss something or did you test after float adjustments?
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Ah ha, I dug deeper and found that you had the same problem in 2008 and fixed it with a distributor cap and rotor, and now you say a ZT carb fixed it:

    http://www.classiczcars.com/forums/s...d!!&highlight=


    A lot of folks are trying to help you out but you gotta give us ALL THE DATA ....well just don't cry Wolf.

    Think you got slop in the spindle linking the oil pump to the distributor or in the gear drive off the snout of the crank.

    Get your buddy's Z over, pull the distributors like you did and compare how the tang at the end of the spindle move when wiggled,lifted,turned. Use a dial gauge rigged up to an extension out of the mounting for emperical measurements.

    Quick and dirty test that just came to mind:
    For ease and consistent measurments, use the same distributor on both cars locked down with a dial gauge on the rotor. Any slope in the distributor will be nulled out by using the same distributor. Also repeat this many times throughout a whole revolution of the crank as the problem could be a broken or worn tooth in the drive helical gear.

    Also try cranking with a socket at the crank back and forth while holding the rotor in your fingers to see how the tang behaves/feels between the two cars.
    Last edited by Blue; 01-07-2012 at 11:19 AM.
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  76. #176
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    Well I took her out for a spin and to no surprise the float adjustment did not fix anything, BUT I can definitely rule out the floats not being adjusted...

    So while the engine was warm, I took the plugs out and looked at them and then decided to do a compression test.

    I taped up the pistons in the domes, but like a dummy I forgot to push the accelerator to the floor while I cranked the engine so the butterflies would be open. Still, these are my results

    1 2 3 4 5 6
    175 175 172 178 175 178

    FAr better than I thought. Those numbers were with 5 compression cycles.

    I also did some runs pulling the choke when it was making a popping....This is what happened.

    I was in second gear and slowly gave it gas until I was into the severe popping regime. Then I pulled the choke back a bit where I knew the jet tube was being moved down. The car surged forward and started to accelerate again, but started popping again at almost 6000. The car seemed to like the enrichment.

    This led me to think the car was running lean despite the popping noises it is making... so I pulled the plugs after driving home normally..

    Here are the results.

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    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  77. #177
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    Have you tried capping off the brake booster and going for a spin to see if that effects the condition?

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    I thought it sounded like it was running lean by your description-thus why I was pushing for an enrichment of the floats. The plugs look at little white from what I can tell-maybe leaner on the front 3.
    So she felt like she had more power with increased fuel??
    This could also be a vacuum issue, but your vacuum showed strong signal at idle.
    After setting the rear float-did it pass the test of being able to see fuel sitting at the top of the jet with the piston removed??
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    After seeing those plugs and your results from the compression test with the throttle closed I would be looking for a vacuum leak in the intake system!!
    74 260Z late
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    Certainly smells like a vacuum leak.....
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    It points to a vacuum leak that occurs off idle and not to a persistent leak like an intake gasket, vacuum hose, brake booster. One thing that can act that way is the PCV valve. Since he's running no vacuum advance no cap on the ported vacuum port is another.

    Steve

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    Okay, lots of help here, let me address everything I can.

    MY distributor was rebuilt by Advance Distributors, who put all new bushings, seals, and ensured that there was no slop in the timing up to 8000 rpm. The guys is very well respected from what I read from MG and other Datsun guys. I trust his work. With my light on the distributor, it was rock solid up to as high as I would want to rev it.

    Now I have NO idea how solid my oil pump is, OR my crank gears, etc.

    I am going to pull all the domes again, and try some straight 30 wt per recommendations, as one last ditch for the carbs. I will put the SM needles back in while I am doing that.

    Then I am going to plug the brake booster (which I just replaced with a new one this year) and drive it and then plug the PCV and drive it. I finally got a plug for it.

    After that, I will pull the valve cover and have a look at what is going on there.

    Blue, I did not mean to try to confuse or 'cry wolf'. I am keeping track of a huge amount of data and I do at times forget to report in so to speak. When I first got the car it did in fact NOT rev at all past 4500 rpm, at part throttle, full throttle whatever. A new cap and rotor and actually timing it to 5 degrees BTDC like the factor recommends fixed that.

    To the degree this problem may have always existed is tough, as for the first 2 years, I really did not push the car super hard, so it may have always been there.

    What I am glad to see is even and high compression numbers on my car.

    I do not know how many PSI it should have stock. I ran another compression test on it with the butterfly open and it came up to 182 +\- 2 psi on all the cylinders.

    It is possible I have a bad brake booster, or a leak somewhere that only arrises under load. But the brakes work splendidly.

    I have to admit, this has all the symptoms of a vacuum leak.

    Again, I am sorry for any confusing info... The cap and rotor did let me rev beyond the 4500 rpm wall for the first time, that is true, but the Ztherapy carbs allowed me to run powerfully above 4500 rpm for the first time.

    But blue, you may actually be 100% correct in the end.
    Last edited by Zedyone_kenobi; 01-07-2012 at 03:34 PM.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  83. #183
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    Your cylinder compression levels are great-don't even give that another thought.
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    You guys have been a huge help! I mean huge. I cannot thank you enough. I am going to stop posting results for a while and get my O2 sensor installed. I think my post has generated a little discontent from somebody whom I respect immensely in the Z community. I am going to get out my FSM and trouble shoot this as completely as I can before I bug the good gurus here. I thought I had done that before I posted the first time, but just to be sure, I am going to triple check.

    Again,

    steve911
    madkaw
    blue
    doradox
    Captain Obvious
    5thhorseman
    Diseazd
    30 Ounce
    and anybody else I have missed

    And anybody else I may have missed. YOu guys are all 1st class. Always have been. I am going to stop hogging the resources of this board until I have something worth while to report.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  85. #185
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    Cant help but report results...

    plugged the PCV and the booster out of the manifold, same issues. If it is a vacuum leak it is from somewhere else. All bolts are torqued. I did put back in the SM needles and while I did that I cranked down the fuel mixture as far as I could...about .205 inches until it hit the stoppers. I had the domes and pistons out and the fuel was definitely below that... as it should be. But how far below, not sure until I can get the stoppers out to use 30 Ounces technique. While I was at it, I put 10w30 per the FSM recommendations in the carbs. Will drive it when the rain clears up.

    If that does not pan out, then I will declare victory over the carbs and start measuring how much slop is in my mechanical drive that spins my dizzy. Oh after I get my O2 gage set up. I will probably pull the valve cover off Monday just to have a look around.

    Sorry to keep this going,
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  86. #186
    Supporting Member Diseazd's Avatar
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    Zedy.....One more thought. I know you replaced the distributor with Steve's with no change, but my guess is you still used your distributor cap. Cracks in a distributor cap or rotor sometimes can be almost invisible. Have you tried a new cap and rotor? A hairline crack in the rotor or distributor cap can leak voltage at high RPM causing symptoms similar to yours. Just a thought. Guy
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    Registered User madkaw's Avatar
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    That's what I suggested and I got that idea from googling!!
    Steve
    71 240z,bw-5sp 2.4-40 over,balanced,e-88,big valves,ported&polished, stage2,header, triple Mikuni's 40's
    3.90 Subaru STI LSD

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    Supporting Member Zedyone_kenobi's Avatar
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    NO we actually switched the entire cap / rotor / dizzy as a whole unit.

    I had already tried a new cap and rotor a while back. I did as much common sense trouble shooting as I possibly could in the past few weeks before I started this thread in frustration.

    I am winding down to the last few ideas that I can possibly use on the carbs. I have checked every measurement possible.

    The kicker is the part throttle nature of it all. What would cause this issue at part throttle but not at WIDE OPEN THROTTLE. The PCV and brake booster were not leaking.

    I thought maybe worn throttle shafts that at part throttle that allowed a leak (unmetered air) into the system at half throttle, but not at WOT. But the bearings Z therapy puts in should have eliminated that as a possibility. I need to get on the ball with the O2 sensor and stop messing around chasing my tail.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Supporting Member 240dkw's Avatar
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    Zedyone: If you are going to start looking for a voltage leak do not forget to replace the two condensers on the ignition system. The one for the points and the noise suppression one on the coil if you have not done so. These can test good on the bench but leak or "spill over" at a higher voltage. This was the problem Arne had with his ignition and fixed it by removing the one at the coil.
    Dan

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    Supporting Member Zedyone_kenobi's Avatar
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    The one for noise suppression at the coil is in fact removed. I will check to see if the one for the points has been removed, since I am running a pertronix.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

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    Quote Originally Posted by Zedyone_kenobi View Post
    The kicker is the part throttle nature of it all. What would cause this issue at part throttle but not at WIDE OPEN THROTTLE.
    Yeah, that's what's really got me stumped. I had the exact same thing but it was because I was lean at midrange due to the carb mods I made and the needles I was running. I switched to the N-27's and it went away. And you're running a richer needle than I am on my 260. Sounds like you're lean, but you shouldn't be.

    Wish I had your silver bullet!

  92. #192
    Supporting Member Zedyone_kenobi's Avatar
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    I think the key to this is not to get stumped.
    I feel like my car is a patient on HOUSE,

    Some crazy ailment that I have to try half a dozen things to fix before some obscure thing triggers a eureka moment!

    Still I cannot thank everybody enough for their time and energy replying to my dissertation of a post!
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  93. #193
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    Fine. Then I'm not stumped.

    I just don't have any suggestions at this time.

    If you were anywhere near me, I'd loan you another pair carbs to try. Sure, it would be a shotgun approach, but it would help narrow the field so much that it would be worth it.

  94. #194
    Registered User Bonzi Lon's Avatar
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    Quote Originally Posted by Zedyone_kenobi View Post

    I thought maybe worn throttle shafts that at part throttle that allowed a leak (unmetered air) into the system at half throttle, but not at WOT. But the bearings Z therapy puts in should have eliminated that as a possibility. I need to get on the ball with the O2 sensor and stop messing around chasing my tail.
    A quick but messy trick. Get some very thick high temp grease and run a good size bead around each of the throttle shafts where air COULD enter. The grease should close off any air or suck it in.

    Bonzi Lon
    1973 HLS30-168500
    1968 SPL311-18100
    1969 HLS30-000110 SOLD Shipped to Dubai UAE
    CZCC#11300

    Ones and Zeros

    "We drive only blue cars." Dishwalla

  95. #195
    Supporting Member Zedyone_kenobi's Avatar
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    A glimmer of HOPE>>>

    I put my carbs back together (SM needles back in) with the only difference being that I put in some 10w-30, and she ran VERY well this morning. I was able to push her at part throttle easily to 4500 rpm, without the slightest hint of a pop. When I pushed it past that, I got some minor pops, but 10w30 did make an appreciable difference.

    I am taking her in to the mufler shop today to get the O2 sensor bung welded on and I will finally know where I am running. I am also going to do a full test on my brake booster check valve tonight. I will report back later...

    Having good O2 readings will be very informative and hopefully helpful.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  96. #196
    Registered User doradox's Avatar
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    Just remember that an O2 sensor senses O2 in the exhaust and not the F/A mixture entering the engine. Incomplete combustion can give readings that are not reliable from a mixture standpoint.

    Steve

  97. #197
    Supporting Member Zedyone_kenobi's Avatar
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    Understand completely. Like any data you have to know its limitations.
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  98. #198
    Supporting Member Zedyone_kenobi's Avatar
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    O2 sensor bung installed.

    now to wire up my Innovative sensor and we can start to get some readings!
    1971 240Z HLS30-38691
    93.9% done and getting better every day
    Now with 100% more DATSUN SPIRIT L28 Power
    1968 Datsun 2000 SRL311-03416

  99. #199
    ZCCIV Webmaster motorman7's Avatar
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    The suspense is killing me

    HLS30-02614 in the Cocoon
    HLS30-40147 Very Yellow Daily Driver
    HLS30-40498 Next resto
    SPL311-27444 It lives
    http://www.rcdeng.com

  100. #200
    Registered User het976's Avatar
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    Not to hi-jack the post, but..

    What you are dealing with is very much the same thing I am experiencing, except, I only notice it in 2nd gear. As I bring it up to 4500 it runs well, but when I tip in a little more throttle, it just runs flat and burbles and pops and makes no power...lift off the throttle a little and it clears up and runs fine...nail it and it pulls fine to the redline, although the tach does some pretty wild bouncing as I reach 7K.

    It seems like SU issues, except when it is running flat, the tach bounces from 4K to 5K then 3.5K to 5.5k and so on...if I hold it there eventually it will bounce from 0 to 7K... This makes me think it is electrical or some strange combo. I have a ZX dist on a 2.8L with a mild cam and header, running ZT rebuilt carbs with SM needles. The tach is the stock 240Z and I am thinking this may be part of my issue. The engine has about 1,000 miles on it and has run more or less like this from the start.

    It is drivable, but just not clean.

    I have a lot of troubleshooting to do, based on what I read here before I ask for help, but I thought I would post to add in my experience.

    I am going to switch to an old set of stock SUs and see if it clears up the problem, then change to a 280 tach, then drop in an LS3, in that order…lol
    bought her in 1977, sold her in 1997..found it on eBay 2006...Welcome home.

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