Results 1 to 38 of 38

Thread: Weird dysfunctional SU carb issue, rebuilt and floats reset going on 8 times now.....

  1. #1
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Unhappy Weird dysfunctional SU carb issue, rebuilt and floats reset going on 8 times now.....

    When setting to idle speed, I can't get the rpms to go below 1550, else the engine will just die and chug smoke out the carbs when it dies(seems to reverse rotate a little when it does that). We've rebuilt the carbs and adjusted the floats going on 8 times now per the directions of the SU carb builder dude with the video, and it STILL does this. I'm at a loss. The car has a new distributor in it with the GM module conversion, and I've both based timed it and checked the 3k rpm mark too, everything there is in order, so not sure what it is. Set valve clearances when I changed the valve cover gasket. It's not putting out the exhaust and the vac readings are stable, so not a burnt valve. Brand new fuel pump installed, new lift pump, filter, etc etc etc. Been dealing with this for a LONG time(over a year) on a constant basis, so anything that could be checked/changed for maintenance has been done. WIT'S END BOYS AND GIRLS!!!

    -Mike.

    Ps. Thanks ahead of time for any/all suggestions. Before I removed the carbs to clean(lotsa sludge in the bowls), I actually was able to drive this thing the 2hrs home from where I bought it......you just don't know how many times I've watched and rewatched that SU tuning video.

  2. #2
    Nova Scotia,Canada,Earth Blue's Avatar
    Member ID
    CZCC-7641
    Join Date
    Jan 2005
    Location
    NS
    Posts
    4,085

    Default

    Are the jets sticking due to the chokes? The cable and grunge can cause problems.

    Separate the choke lever from the jet, disconnect the fuel line to the jet, then pull out from the bottom of the carb and clean the jet and orifice where it slides up and down.

    Here is a recent clean from an Austin Z
    Attached Thumbnails Attached Thumbnails Click image for larger version. 

Name:	Nozzles.jpg 
Views:	611 
Size:	98.3 KB 
ID:	64163  
    Last edited by Blue; 06-28-2013 at 10:39 AM.
    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.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  3. #3
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Yes, we have completely disassembled and cleaned every part every time we take them down to check and readjust float levels. These are the round-top SU carbs also, forgot to mention in the original post, off my 72 240z.

  4. #4
    Barn Find Daily Driver Captain_Zeros's Avatar
    Member ID
    CZCC-21373
    Join Date
    Apr 2010
    Location
    Kirkland, WA
    Age
    30
    Posts
    316

    Default

    If you've already checked everything then I'm down to grasping at straws, but what method did you use to adjust your float levels? On my Z I had far more luck adjusting with the sightglass method using a piece of clear tubing than trying to use the "hold the lid outside of the car and blow through a tube and move stuff around with a ruler" method.
    It's also possible you have a fat vacuum leak at the carb gaskets or the throttle shaft, I guess.

  5. #5
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Exactly, nothing is making sense here.....I've been having this exact same problem since I joined the site, surprised my patience lasted this long to be honest. All gaskets on the engine(minus head gasket) have been replaced. I used the method of setting the lids on top of a small pint jar and slowly filling via syphon pump to set float levels. It's a tedious process, but it gets the levels dead-on. The only reason I haven't sent both sets of these carbs off to be redone, is at first I couldn't justify the cost of him doing them(rest of car wasn't in very good shape).....but it grew into the "You cannot defeat me!!!" routine.....now I'm getting close to sending them off lol.

  6. #6
    Registered User Jarvo2's Avatar
    Member ID
    CZCC-26781
    Join Date
    Mar 2012
    Location
    Plainfield, IL
    Age
    41
    Posts
    238

    Default

    Are you still running a voltage regulator? I was having similar issues and just upgraded to a ZX internally regulator alternator along with the jumpers required...everything is running much much better now!
    Dave
    Windy City Z Club (Chicago)
    1972 240z, restoration in progress
    http://jarvas240z.blogspot.com

  7. #7
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Yeah I'm running an AD244 alt with a v-belt pulley swap to an external regulator with high amp internals, ampere gauge swapped to high-amp ampere gauge and volt meter combo gauge, and everything seems to be doing right, it peaks at 15.2v with no accessories on, which is still in the green range.

  8. #8
    Registered User Gary in NJ's Avatar
    Member ID
    CZCC-21253
    Join Date
    Mar 2010
    Location
    Amongst the twisty roads
    Posts
    1,057

    Default

    What is the condition of the Grose Valves? You might have one that doesn't fully close, allowing an over-rich condition.
    Gary
    Guardian of HLS30-91415
    Previous Owner of a 10/70 240Z ('83-'85)

  9. #9
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Well we're still using a kit we got a couple years ago that included new valves, we've run the engine with the drain screws removed and the "hollow screw to clear vertical tube" method to make sure the level doesn't go too high and it always stays within a millimeter or 2 of where we adjusted it. So I don't think it's bleeding past, unless it just randomly sticks when we aren't testing the level. The way it dies confuses the heck outta me too, when it dies it stops rotating, then it rotates backwards spewing smoke out the blowback holes in the carbs. I'll take a video in a bit showing what it does when it dies.

  10. #10
    Rust Free'ish zKars's Avatar
    Member ID
    CZCC-12190
    Join Date
    Jul 2006
    Location
    Calgary, AB Canada
    Posts
    1,256

    Default

    Pull the domes and make sure that both jets are flush with the bridge with the adjusters all the way in, or at least both are the same and close to the top. Did you remove the needles from the piston? Back in the right place? You are definitely running rich.
    -----------------------------------------
    Jim
    73 240Z HLS30 149331
    69 510 PL510 77603

    www.zKars.com
    www.calgaryzclub.ca
    Reference materials
    www.xenonS30.com

  11. #11
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Here's how she does when easing off gas, started shaking a little at 1800rpm and fell on it's face at 1700rpm.

    Last edited by mr mikey; 06-28-2013 at 01:22 PM.

  12. #12
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Quote Originally Posted by zKars View Post
    Pull the domes and make sure that both jets are flush with the bridge with the adjusters all the way in, or at least both are the same and close to the top. Did you remove the needles from the piston? Back in the right place? You are definitely running rich.
    The needles are in the same place, but when fully warmed up, it does get a teensy bit of sooty exhaust when you get on it good with no load on engine, so I might play with the height of the needles a little.

  13. #13
    Registered User Jarvo2's Avatar
    Member ID
    CZCC-26781
    Join Date
    Mar 2012
    Location
    Plainfield, IL
    Age
    41
    Posts
    238

    Default

    definitely running rich at idle....any chance the SMOG equipment you have installed is causing a lean condition below a certain RPM?
    Dave
    Windy City Z Club (Chicago)
    1972 240z, restoration in progress
    http://jarvas240z.blogspot.com

  14. #14
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    The smog stuff is actually unhooked at the source, only using blocked tubes to seal off any leaks, I haven't gotten around to making the blockoff plates for everything yet, as this current issue is draining every bit of mental capacity I can put towards the car lol. I'll get some nipples to cover all the spots, or if you think maybe the parts are internally broken and hemorraghing through to the exterior, like a vac leak thru the housings.

  15. #15
    Registered User Jarvo2's Avatar
    Member ID
    CZCC-26781
    Join Date
    Mar 2012
    Location
    Plainfield, IL
    Age
    41
    Posts
    238

    Default

    Seems like something isn't flowing as it should. Here's what I ended up doing temporarily. On the air galley, a black-pipe cap fits perfectly.

    Click image for larger version. 

Name:	IMG_0684.jpg 
Views:	345 
Size:	150.6 KB 
ID:	64164
    Dave
    Windy City Z Club (Chicago)
    1972 240z, restoration in progress
    http://jarvas240z.blogspot.com

  16. #16
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Have you tried to alter timing-retard it? Does it fire up easy everytime? It seems that the timing might be way advanced.
    Linkage-what have you done to eliminate that possibility?
    What's the history on the engine? Have you ever heard it run right, or did you buy this and started out this way?
    What year car and engine?
    What distributor are you running?

    I have no answers, just questions
    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

  17. #17
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Quote Originally Posted by madkaw View Post
    Have you tried to alter timing-retard it? Does it fire up easy everytime? It seems that the timing might be way advanced.
    Linkage-what have you done to eliminate that possibility?
    What's the history on the engine? Have you ever heard it run right, or did you buy this and started out this way?
    What year car and engine?
    What distributor are you running?

    I have no answers, just questions
    I thought the same thing about the timing, especially the way it reverse rotates, but it not hard to crank(actually very easy to crank).....my camaro is base timed at 18degrees advanced, so I know how an advanced engine sounds when turning over lol. The linkage has been checked for slack and worn joints and such, it all seems to be fine. I can spray wd40 around the throttle shafts to check for revving from vac leaks and the idle speed never changes(unless I accidentally overspray into the barrels haha). When I bought it, I was able to drive it the 2hrs to my house, but it chugged and rolled coal when I tried to pull any real hills. Tore the carbs down per the video and found a bunch of crud in the bowls, so I went nuts with a toothbrush and scrubbed all the internal components, and readjusted per the video.....it hasn't been right since. Car is '74 260z, Engine is '74 260z, carbs are '72 240z. Distributor is a "NOS/OEM" electronic ignition distributor listed for a 260z with the GM electronic control module.....it had the Crane(Allison) Fireball 2000 or whatever it's called, but it kept going thru control modules(found later that the setups are finicky when it comes to quality).

    I have all the answers, except the one to my question lololol.

  18. #18
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    How do you know you are close on timing? You can't check static at 1800rpm, so what advance to you show at your present idle?
    Sounds like your effort needs to be somewhere other then carbs at this point.

    There was just a 7 page thread with similar issues and it turned out to be timing.

    The fact that you know little about this engine, someone could have clocked the dizzy drive wrong.
    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

  19. #19
    Barn Find Daily Driver Captain_Zeros's Avatar
    Member ID
    CZCC-21373
    Join Date
    Apr 2010
    Location
    Kirkland, WA
    Age
    30
    Posts
    316

    Default

    Maybe a little off topic, but the one time I ever had reverse rotation and puking smoke out the carbs was when I accidentally clocked my dizzy 180 degrees out like an idiot... then again it wouldn't run at all that way. It seems like it runs pretty well for the first 40 seconds or so of that video, so I'm real curious what the issue is. Do you have a different distributor/ignition-module(points even?) you could try? It might be confirmation bias but whenever I hear about HEI ignition modules there is a problem involved (then again nobody ever complains that their ignition is working perfectly either.)

  20. #20
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Quote Originally Posted by madkaw View Post
    How do you know you are close on timing? You can't check static at 1800rpm, so what advance to you show at your present idle?
    Sounds like your effort needs to be somewhere other then carbs at this point.

    There was just a 7 page thread with similar issues and it turned out to be timing.

    The fact that you know little about this engine, someone could have clocked the dizzy drive wrong.
    I set it per the instructions for the dizzy. Set the dizzy so the rotor is centered on the #1 plug wire contact, align the dizzy to the 0 mark on baseplate, stab dizzy so baseplate mounts to engine when balancer mark is aligned with 0 mark on timing tab. Then loosen dizzy hold-down and rotate the dizzy so it's pointing at 9 degrees advanced on baseplate, then lock-down dizzy.

  21. #21
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Timing light?
    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

  22. #22
    Nova Scotia,Canada,Earth Blue's Avatar
    Member ID
    CZCC-7641
    Join Date
    Jan 2005
    Location
    NS
    Posts
    4,085

    Default

    Hardway and I measured the height of the fuel bowl roof from the gasket surface, I think it was 3.4mm so the 23mm down from the edge of the fuel bowl becomes 19.6mm down. We set the fuel level for this and the jets had to be set a little higher to optimize.
    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.


    John Ruskin (1819 - 1900)



    ZCars in Eastern Canada seaport ready for shipment to Europe

    http://ZSportCanada.com


  23. #23
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Quote Originally Posted by madkaw View Post
    Timing light?
    No, not on the base timing setting, it said in the instructions that it wasn't necessary, because the adjustments were fully mechanical. I did use a timing light to check max advance at 3500rpm, and it is sitting on the 36 degree mark on balancer.

  24. #24
    Registered User tlorber's Avatar
    Member ID
    CZCC-20299
    Join Date
    Oct 2009
    Location
    Los Angeles
    Age
    54
    Posts
    1,190

    Default

    Do you have access to any spare carbs that you could bolt on?

  25. #25
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Can you elaborate more about what's blocked off and do you have anymore pictures showing the induction system ?


    Quote Originally Posted by mr mikey View Post
    The smog stuff is actually unhooked at the source, only using blocked tubes to seal off any leaks, I haven't gotten around to making the blockoff plates for everything yet, as this current issue is draining every bit of mental capacity I can put towards the car lol. I'll get some nipples to cover all the spots, or if you think maybe the parts are internally broken and hemorraghing through to the exterior, like a vac leak thru the housings.
    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

  26. #26
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Quote Originally Posted by tlorber View Post
    Do you have access to any spare carbs that you could bolt on?
    I borrowed a pair from my buddy off his 240z, and they did similar, but what they would do is let you idle it down to 700 and stay running fine for a while. Then after about 5min or so, it would just act like you turned the key off(with the exception that it would still reverse rotate and spew smoke from the relief vents of carbs).

  27. #27
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Quote Originally Posted by madkaw View Post
    Can you elaborate more about what's blocked off and do you have anymore pictures showing the induction system ?
    Yes, I can take more pics. All vacuum hoses that lead directly to a vacuum source have been blocked off, so any/all accessories you see with vacuum hoses are just dead hoses. I'll eventually mill down the blockoff plates I made for all the components and install them, just been super busy with work. Also, the heater crossover channel(preheats manifold)has been blocked off internally. I need to figure out how to get the screw-in hose barbs out to replace with brass plugs.....they look like they're in there pretty good, didn't want to break one.

    I'll get more detailed pics when I get back, gotta go outta town, cousin is getting married in Indiana. I don't like that drive.

  28. #28
    Registered User
    Member ID
    CZCC-27135
    Join Date
    May 2012
    Location
    Sacramento, CA
    Age
    71
    Posts
    20

    Default

    I couldn't help notice that you were measuring 23mm below the top edge of the bowl.
    According to the factory manual, the 23mm starts from the bottom of the float bowl
    lid. Turns out the distance from the bottom of the float bowl lid to the bottom of the
    lid is exactly 3mm, if you don't count the thickness of the gasket, the proper level
    for the fuel would then be 20mm below the top edge of the bowl. Nobody has ever
    said how accurate this has to be, but we know if the level is too high, we get a
    rich mixture.

    I re-read your comment, I measured 3.0mm, you measured 3.4mm, close enough.

    It's so much easier to just measure 20mm down from the edge, why is everybody
    stuck on 23mm?

    Jim

  29. #29
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Well I stopped trying to figure it out for now, got alot of body work to do. But if someone could confirm their advance at these 3 rpms, it would give me an idea of which way to adjust. With the vac advance hooked up, in neutral, no engine load. 18 degrees @2200rpm, 15 degrees @2000rpm, 12 degrees @1800rpm. If I adjust idle to 1700, you can hear it go from a perfectly smooth idle to an every so often hiccup, like it's either loading up or ignition is being cut for a split second.....then adjusting down to about 1650rpm will make it die and do it's reverse rotate thing.

    Floats are set per Blue's post, and that's with the jets set to 2 turns down.

  30. #30
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Well, I found something interesting. When I began to idle it down, the moment it starts acting up is when the spark becomes erratic, then I lose spark and it stalls, then regains spark the second it begins to reverse rotate. Talk about weird.

  31. #31
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Ok, I reversed the polarity on the ignition control module, where it reads the spark trigger, and it fires right up and idles fine(with a slight hiccup every so often). So used that time to make sure carbs were set, advance was correct, etc etc etc. Only prob with running reverse polarity is you cannot rev it any, it'll only idle(set idle to 700rpm). Reversed the polarity back to correct, and it still does the same thing. Base timing is at 9 degrees advanced, advance tube plugged. Everything is doing right, but now have an issue. My old service manual is well used, especially in the ignition areas. I need to know what to set the hall effect trigger to, as far as gap is concerned. I cannot see the numbers, too much smudge. Local guy told me that I can't just set it to almost touching, without touching, because it would cause the ignition module to see too many breaks in the magnetic field, and the spark control would be all over the place. So I guess I can't set it like I do the gap on an old magneto engine.

  32. #32
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Just make sure to use brass feeler gauges . Maybe .010
    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

  33. #33
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Ok, set to .010", and it idles down to about 1300 then loses spark. Set to .008", and it's down to about 1000rpm, any lower and it loses spark. I tried adjusting to .006", but the very bottom of the "fins" on the dizzy shaft are touching the pickup. The fins look like they're straight until the very bottom, and they stick out a little. I figured I'd been ripped and gotten sent a worn out dizzy, so I ordered a new one and the fins are the exact same way. Anyone notice their electronic dizzy's "6-point star piece" on the shaft being shaped like this? The gap throughout top to bottom is the same, except the very bottom, each "fin" of the star piece has a lip that sticks out a little farther?

  34. #34
    Registered User
    Member ID
    CZCC-23125
    Join Date
    Dec 2010
    Location
    Spartanburg, SC
    Age
    50
    Posts
    468

    Default

    Madkaw, why brass?
    C

  35. #35
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Non-magnetic
    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

  36. #36
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Ok, I kept going down in size of feelers until it would idle at 400rpm, so I'm guessing the size it requires is .004". I had to mill the bottom lip off each fin so it wouldn't scrub the pickup, but everything seems to work fine now. Thanks a bunch, this thread can be closed now.

  37. #37
    Registered User madkaw's Avatar
    Member ID
    CZCC-7622
    Join Date
    Dec 2004
    Location
    bloomington IN
    Age
    57
    Posts
    2,288

    Default

    Just goes to show to keep an open mind when troubleshooting.
    Not sure why you want to idle at 400rpm?
    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

  38. #38
    Registered User
    Member ID
    CZCC-22836
    Join Date
    Nov 2010
    Location
    Central Mississippi
    Posts
    58

    Default

    Quote Originally Posted by madkaw View Post
    Just goes to show to keep an open mind when troubleshooting.
    Not sure why you want to idle at 400rpm?
    You're so right, can't believe it wasn't carb related after all lol. I don't idle at 400rpm, but I also didn't want it stalling right below idle speed. I've got it set to idle when fully warm at 700rpm, but if I'd set the gap to 700rpm(.006"), then it would stall the second it started to go below that. I guess I could've set it to .005"(mathematically stable down to 550rpm), but my gauges go from .006-.004", no .005" feeler gauge. I guess what I did, was give myself a 300rpm buffer zone below idle speed, as a precautionary measure.

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. How do I reset password ?
    By 9teen7t240z in forum Open Discussions
    Replies: 3
    Last Post: 03-05-2012, 11:53 PM
  2. Weird 240Z steering issue
    By AX75F92 in forum Suspension and Steering (S30)
    Replies: 0
    Last Post: 02-22-2012, 01:19 PM
  3. SU Carb Idle Issue
    By duffman in forum Carburetors (S30)
    Replies: 4
    Last Post: 11-08-2010, 08:06 AM
  4. Weird Headlight issue
    By BlkPrl in forum Electrical (S30)
    Replies: 2
    Last Post: 10-24-2010, 10:42 AM

Bookmarks

Bookmarks

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •