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Thread: Problematic Running - Advice if you have some.

  1. #1
    Registered User oranngetang's Avatar
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    Default Problematic Running - Advice if you have some.

    I'm sure this has been covered in other help me threads, but I've read through a dozen or more and have consolidated all of the information that pertains to my setup. I'm beginning to wonder if perhaps my distributor is going. Any advice is welcome, I appreciate the input.

    The problem that I'm experiencing is while the car is occasionally very smooth up to 6500rpm or so, after a few minutes of idling, it'll become jerky and misfire. The problem seems to have no easy cure. Sometimes if I shut it down for a few minutes, everything is fine again, sometimes it's the opposite. I assumed fouling from carbon may be causing this, since when it runs poorly, it will occasionally give a small backfire from the tail pipe. I'm guessing the misfire is letting unburnt fuel into the exhaust where it eventually finds ignition.

    I have balanced and tuned my ZTherapy 4 screw carbs as per the Just SU video, using a uni-syn meter. It seems no matter what, the engine only runs if the conditions are extremely rich. I'm currently nearly hitting the stops on the mixture adjustment screws. I pulled the float bowl lids off and adjusted the needle valve to roughly 18mm from top of float to bottom of lid using the blow and listen technique... I can't see how anyone gets very accurate results from that. Anyway, the car seems to run the same, with just less carbon smoke as I lean it out to a certain point, and that's where I've left it. I'm talking a minimum of 5 turns to even get an idle out of it.

    Ignition wise (and this might be a big part of the issue), I'm running stock dizzy with points. I opened the plug gap from 0.32 to 0.39 on the stock NGK plugs and noticed a considerably better burn. Coil is an MSD Blaster 0.7Ohm, with 0.8Ohm resistor that came with it for use with points. This seems like it may not be enough resistance to me. That would give 8A instead of 4A (3Ohm) at the dizzy, unless I'm confused. I installed a new set of points and set that gap to 0.18".

    Timing? Well, I drew a line on the harmonic dampener and set the timing to 10BDC, total advance is 60BDC, so I'm gaining 50 degrees from the mechanical / vacuum at about 3800rpm. The idle was rough, so I increased the timing to 15BDC and everything is smooth, without detonation. My line is probably off.

    I have a pertronix ignitor on its way for Friday to give it a try. There seems to be mixed reviews if one can run it without a resistor or not. I'll give the manual a read.

    Any thoughts or where to startover? I've fought with this for a week, tuning everyday until I find a happy spot and then all by itself it just starts misfiring and lurching all over. I've even tried pinching off the fuel return line to see if it's a pump issue. Stock mechanical pump btw.. Power-wise, when it's running decently, it'll run happily up to about 80mph, and then drag its ass to 115mph and no faster. I'm not sure that's typical or not.

    Stock L24, A cam, P30/E88 head, Ztherapy 4 screw with needle valve, not grose jet, headers, stock air horns, stock ignition other than the coil, new plugs, wires, cap.

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    Registered User oranngetang's Avatar
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    I should also mention, #4 plug is always wet fouled when all others are dry. Number 1 is always tan and clean, no matter what... Whatever that means.

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    I suggest you start by putting a vacuum gauge on it, both when cold,and hot.

    Your symptoms might be explained by a simple vacuum leak, intake manifold gasket, etc. One that intermittently seals itself up.

    Vaccum readings could point you to this and other possible problems.

    Have you verified spark at #4, is it as bright and long a spark as, say, #1?

    If you have no experience using a $15 vacuum gauge, visit this website.

    http://www.secondchancegarage.com/public/186.cfm

    When it's running rough I'd spray all around the intake manifold, brake booster lines, etc. with brake cleaner while listening for an increase in RPM.

  4. #4
    Registered User oranngetang's Avatar
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    Sorry Wade, my reply is long overdue, partly because winter started for us at about the time I started this thread.

    I have the Z back on the road for this year, and have been doing some trouble shooting. It seems that until the engine is well warmed up, it really doesn't want to drive at all unless the choke is pulled. Once I've had it flat out for a mile or so, it starts to drive absolutely fine, though that #4 is still getting oil in it, and the smoke is visible when shifting gears.

    I currently have the carbs synced using the unisyn tool, with a slightly high idle of 1100rpm. With a lower idle, #4 fouls up fairly frequently.

    I'm running a Pertronix Ignitor in the factory dizzy, with an MSD Blaster coil and ballast.

    Once the engine is lively, I can take it for a good run, clutch in, engine off, and pull plugs. All plugs are tan and clean at the electrode, but with evidence of carbon on the threaded housing. Number #4 plug is always wet along the bottom threads.

    Compression on a warm engine is 150-160PSI on all cylinders, the gauge I'm using isn't anything special, and I think with the length of hose it has, 170lbs might be a more accurate. #4 seems to always have 5lbs more than the other cylinders, probably because it is wet.

    Timing? I found top dead center the best I could for now, and marked it out. With vacuum advance disconnected and at an 1100rpm idle I read 28* BTDC, engine at 4000rpm is 45* or so, so clearly my mark is off, or the dampener has separated, or I suppose the centrifugal is stuck at 28*. If I keep the light on the engine and rev it, from an idle the mark retards before advancing. I have drawn a line across the dampener to see if it walks out. If I retard the timing 5 degrees from where I am, I loose all bottom end and get an occasional backfire at intake. I would assume based on that, I'm running close to 8* BTDC and 25* total, unless the 28* mark is accurate. Oddly enough, to get to this point I need to turn the distributor as far as it will turn to advance, so maybe it's out a cog.

    I have not yet picked up a vacuum gauge that will work with this. I need to do some tinkering, or buy a new gauge.

    I tried the trick you mentioned with some starting fluid and brake clean without anything obvious. My brake booster lines are newly replaced, the booster works well, and if I disconnect the brake booster line the engine revs upwards, so I think the vacuum is good on that end of the manifold. Other than that port and the PCV, the vacuum advance is the only other place for it to leak, since I have a smoothed balance tube and NO emission equipment.

    Spark is good on all plugs. I made an adjustment to the gap on #3 and #4, because it was scattering around the electrode, and now everything looks good.

    Once the car is warm and running well, it drives and pulls nice. Will walk up to 100MPH fairly well, with no flat spots, just somewhat lacking in power below 2000RPM. It feels like it pulls best between 4500 and 5500RPM and then the power starts to drop off. If you've ever driven a VTEC Honda, IE: B16A in a late 80s CRX, this is exactly how it behaves.

    Until I really give the car the beans, it will run like crap and not idle, demand choke, stall, and so on. Basically it demands to be rich when its cold, and if the choke is anywhere other than all the way (you can smell gas), it will lurch and spit and pop, and will not accelerate. Even if the engine warms up, and I havn't given it a good run flat out, it will continue in this manner.

    This is a huge post, I wish there was less to make you guys read.

    My first question is... with a decent compression test, is it possible my oil leak in #4 is coming from the head? I set the valves last year, between a half of 1 thousandth and 1 thousandth inch tighter than factory specs on a cold engine. Doing this removed a lot of valve clatter, but perhaps I should redo on a hot engine? If I pull off the valve cover, what will I want to be looking for oil consumption?

    I feel like I should not drive this car anymore until I have this sorted out. OR say the hell with it and rebuild this thing if necessary.

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    Registered User oranngetang's Avatar
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    Pics of plugs....


    After a high speed, warm running sprint, clutch in and ignition off.
    Click image for larger version. 

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    After the drive home, with idling at lights and pulling into garage.
    Click image for larger version. 

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    A local shop advised that I probably have a stuck ring in #4 from the excessive carbon in the engine from sporadic and rich running, probably why that plug keeps becoming fouled. He recommended Seafoam and carb cleaner. I asked if it was his engine, what method would he choose. The recommendation was to soak the cylinder in carb cleaner over night, filling it, if it drips away.

    I decided to do both, and ran seafoam through the engine as directed, later in the evening, drained the oil, left the plug out and pulled the #4 spark plug. The cylinder took about 1/3rd a can of carb cleaner to fill. I waited 4 hours for it to drain, refilled, and repeated. When my carb cleaner was through the rings and out the pan, I filled the cylinder with ATF for the night. Only a couple of CC leaked over 8 hours. I left the plug out and turned the crank with a socket to get the ATF out, and then cranked with coil disconnected to clear it.

    I spent most of today pulling out my A-type trans and finding my rear-main leak looks to be the tranni input seal, or perhaps it is indeed both. I installed a '72 B-type I picked up a few months ago and fired up the engine after refilling with oil and filter. So far no drips. I would take it for a drive and see if it drips, and if this experiment did anything positive to the engine or not, however I can't get the shifter in. I suppose my choices are to cut the floor and notch the console (i'd rather not), or cut, weld and bend the shifter to not interfere with the cutout.

    I'll post results on this, and if the #4 continues to foul in the upcoming days hopefully.

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    Your timing issue is what bugs me. You seem to be all over the place.
    How did you find TDC?
    Have you checked your mechanical advance to see if it's in good shape?
    I would run without vacuum advance for now.
    If run about 12 degrees advance at idle-750rpm
    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 removed all plugs other than #1 and turned engine with a wrench until I felt pressure. At that point I removed the plug and inserted a pier of wire and watch it as I strokes the piston up. Since there seems to be about 15 degrees of crank rotation where the piston effectively stops moving, I made two marks on the wire. One for stops going up and one for stops going down, and then marked the top side of the crank pulley half way in between.

    In going to build a drilled out plug with hose and oil inside to fun this more accurately.

    Do I make the mark on the TOP of the.pulley or do I put the mark where the timing mark poibter is, with engine at TDC?

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    FYI, my $100 b-type is an incredible improvement over my 43 year old original a-type. The shifter mechanism is a huge improvement, and this own appears to have synchros left! Car smokes like hell, I'm hoping it's just oil in the exhaust and I didn't destroy throat cylinder with my experiment.

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    At the pointer
    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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    #4 could be due to a crack in the head. Are you losing any coolant?
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    Not losing any coolant that I have noticed. I've put a couple hundred miles on the car since putting it back together and haven't needed to add any coolant, or noticed any steam from exhaust.

    I'll try for a more accurate mark. I don't knowing the mechanical advance is in GOOD condition, I've nearly checked that I can move it and have lubricated it.

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    What also bugs me is your comparison of engine power to an inline 4 Honda motor. Not sure what your past experience with Z cars are, but these cars are very torque and it sounds like you have none. That coupled to having to run with the choke says to me that your float levels are lean.
    You should probably try to eliminate head gasket issues by getting a coolant tester or some kind of tester.
    Have you also experimented with timing changes? Try advancing without your vacuum advance installed to see how it effects 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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    Quote Originally Posted by oranngetang View Post
    Not losing any coolant that I have noticed. I've put a couple hundred miles on the car since putting it back together and haven't needed to add any coolant, or noticed any steam from exhaust.

    I'll try for a more accurate mark. I don't knowing the mechanical advance is in GOOD condition, I've nearly checked that I can move it and have lubricated it.
    My bad! When I got home I checked the coolant just to be sure ad it was down almost a little. I'll keep an eye on that. Perhaps a rebuilt head is going to be on order soon...

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    Quote Originally Posted by madkaw View Post
    What also bugs me is your comparison of engine power to an inline 4 Honda motor. Not sure what your past experience with Z cars are, but these cars are very torque and it sounds like you have none. That coupled to having to run with the choke says to me that your float levels are lean.
    You should probably try to eliminate head gasket issues by getting a coolant tester or some kind of tester.
    Have you also experimented with timing changes? Try advancing without your vacuum advance installed to see how it effects power
    I wouldn't say my car is very torquey. I've been in a 260Z with L28/triple carbs and it was much quicker. This is kind of an unfair comparison though.

    Taking some advice given here, I double checked my TDC measurement, which I would say is within 1 degree of TDC, and set my timing to 12* BTDC at 850rpm. This dramatically reduced my idle, so I re-synced the carbs using a unisyn, and needed to increase richness on both carbs. On top of that, I disconnected the vacuum lead on the advance and went for a drive. The car idles smoother at 12* with the idle screws opened slightly wider, but drives nearly the same, perhaps with less power than before. I think it's possible I was actually at 20+ BTDC advancement before, which is crazy without detonation

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    Quote Originally Posted by oranngetang View Post
    I think it's possible I was actually at 20+ BTDC advancement before, which is crazy without detonation
    This is assuming that the mechanical/centrifugal, and vacuum advance are/were working. Have you checked timing while revving the engine?
    1976 280Z, with some minor modifications

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    I have pretty much given up on posting from my iphone... I'll try to repost.

    The centrifugal swings rather well, and returns to 'zero' when at idle. It does not appear to be getting stuck anywhere. I think it was giving 18-20 degrees additional up to around 4000rpm, but I'll recheck this afternoon when I'm home.

    Would it be of any help if I posted a short video of the car when warm, at an idle, using GoPro behind my timing light to show RPM vs Total Advance, working up in 500RPM increments?

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