Rough idle and stumble/hesitation when hot

Discussion in 'Small Block Tech' started by ThinRedPaste, May 26, 2018.

  1. ThinRedPaste

    ThinRedPaste Well-Known Member

    I've been struggling with this nonsense for a long while and I haven't been able to correctly diagnose it. I'll do something and it'll go away for like half an hour and then come back.

    The car (69 skylark with 350-2 and th350) starts well cold, and runs good until the water temp gets up to about 170 (slightly before thermostat opens), then it'll start idling rough and missing intermittently at stop lights, and it'll stumble and hesitate badly when i try to start going again, regardless of how much gas I give it. Once in motion for a few seconds it cleans up and runs fine. Also starts hard hot sometimes, but not always. The longer I'm in traffic the worse it gets, and the hotter the weather is the faster it deteriorates.

    things i've tried, not necessarily in this order:
    carb spacer/insulator (not a very big one though)
    insulate fuel line
    replace carb (rochester 2gv)
    replace all vacuum hoses
    tune carb using vacuum gauge
    improve cooling
    replace ignition coil
    tighten bolts on carb and intake
    replace pcv system
    new air filter
    new spark plugs
    disconnect vacuum advance and plug hose (testing a theory that it was too advanced at idle. Didn't pan out, put it back)

    Next thing under consideration is replacing the points and condenser (with a pertronix kit most likely) but I don't know enough about distributors to tell if they're bad.
     
  2. alec296

    alec296 i need another buick

    What about checking points and point dwell? Check the timing to see if it’s low ? Check if choke plate is opening once hot.
     
  3. ThinRedPaste

    ThinRedPaste Well-Known Member

    if anything the choke plate opens too soon. I don't really know what I'm looking at with points which is part of the reason i was thinking about putting in a pertronix kit. Ignition in general is kind of a mystery to me. Also, I don't have a timing light so I have no idea what the timing is set at. Would these symptoms indicate early or late spark, and why would it change with engine temp?
     
  4. alec296

    alec296 i need another buick

    When engine is cold it likes to be rich . And timing would probably be retarded with timing chain stretch .
     
  5. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If you want to work on the car and avoid bringing it to someone who will charge you, then you need the tools that are necessary. A timing light is not optional, get one, you'll need it for this car. You'll also need a dwell meter. Dwell changes timing, so if the dwell is off, so is the timing. Ignition in general is a mystery to lots of car enthusiasts, but it doesn't have to be. Back in 2005, I started this thread,

    http://www.v8buick.com/index.php?threads/power-timing-your-buick-v8.63475/

    In it, I have explained ignition timing basics. I have also answered countless questions about timing and how to use a timing light. Between that thread and the ignition section of just about any Buick Chassis Manual, you should be able to understand it. Guys think it is rocket science:), but it isn't, you just need to want to learn.

    Having said that, what you are describing sounds like vapor lock. The ethanol in fuel doesn't help. What happens is the gasoline can boil in the carburetor and lines. The intake manifold has a passageway that runs under the carburetor. It is meant to help with fuel vaporization in cold weather, but what it does is super heat the intake manifold and the carburetor. The oil companies also change fuel blends in the winter and summer. The winter blend vaporizes easier for cold weather. If you are running any fuel you got before putting the car in storage, it will just exacerbate the problem. Blocking off the exhaust cross over passage can keep the intake cooler.

    Of course ignition timing that is wrong can also make things worse, but you don't know your timing. You can't afford to not know.

    Get a timing light, Sears makes a nice one.

    http://www.sears.com.pr/craftsman-advanced-timing-light/p-00914065000P
     
    Dwayne B and alec296 like this.
  6. rjm

    rjm Well-Known Member

    If you're looking for a timing light, I can recommend the innova brand. The one I got can also read dwell. I had an issue with the bulb, called them up, sent it in and got a new light in about 10 ~ 12 days. Customer support was great. Amazon had the best price when I got mine .
     
  7. ThinRedPaste

    ThinRedPaste Well-Known Member

    if it's being caused by vapor lock, I'm struggling to figure out why. Yeah there's that exhaust crossover, but if that's the problem now then why wouldn't it have been one since the car was made? I've insulated the fuel line, i've put an insulation spacer under the carb, the fuel line isnt getting too close to the exhaust anywhere. it gets closer to the block than i would like, but its the factory line in the factory place, and doesnt seem to have enough extra to try and pull it out away.
     
  8. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    Because the fuel is different, and the engine may be running hotter. Incorrect ignition timing can be one factor that causes the engine to run hotter. You don't know your timing though so we can't even guess.
     
    Last edited: May 27, 2018
  9. ThinRedPaste

    ThinRedPaste Well-Known Member

    So I checked the points, found them burnt, and dropped in a pertronix kit. It's running way better now, but i'm sure it's too far advanced. Acts like it's fighting itself to start and pings under hard acceleration. I got a timing light and i have it hooked up, but I'm still confused. The mark on the pulley is appearing on the passenger side of the engine at idle, with the vacuum advance plugged, but the engine marks are on the driver's side. Is it really THAT far advanced or is something wrong? I'm sure I have it clipped onto the #1 wire. Also, where is the bolt to loosen that lets me turn the distributor, and which way do a turn it to retard the timing?
     
  10. Aaron65

    Aaron65 Well-Known Member

    You have to readjust the timing when you install a Pertronix unit. The bolt to loosen the distributor is right underneath the distributor body on the front cover, and you'll turn the distributor counterclockwise to advance, clockwise to retard.
     
  11. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member


    It could very well be that advanced. The distributor has a hold down secured by a single 9/16" bolt. It is at the base of the distributor where it enters the timing cover. Loosen it just enough so you can rotate the distributor. Turn the distributor clockwise (looking at it from the top) to retard the timing.
     
  12. ThinRedPaste

    ThinRedPaste Well-Known Member

    i cant find any such bolt, nor can i see where the distributor goes in. theres too much in the way. i did find a 9/16 bolt in the top of the front cover itself, but loosening it didn't seem to do anything. does anyone have a picture of it?
     
    Last edited: Jun 2, 2018
  13. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    I didn't say it was easy to see or get to, they make special wrenches to get to it. This is what the stock hold down bracket and bolt look like,

    DistributorHoldown1.jpg

    Some use a big washer and bolt. The bracket or bolt pushes down on the collar of the distributor preventing it from turning. Sometimes even with the bolt loosened, it may be difficult to turn. It's right next to the bypass hose.

    distributorholdown.jpg
     
  14. ThinRedPaste

    ThinRedPaste Well-Known Member

    wow yeah i'll never get to that. my distributor sits way lower than that and the vacuum pod is in the way. speaking of the vacuum pod, i dont think it's going to allow me to turn the distributor enough to retard it as much as it appears to need. it'll hit the bypass hose.
     
  15. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    They make distributor wrenches to get to that bolt. Here is one at Home Depot,

    https://www.homedepot.com/p/Powerbuilt-Distributor-Clamp-Wrench-Set-640580/204505250?cm_mmc=Shopping|G|Base|D25T|25-1_HAND+TOOLS|NA|PLA|71700000034127224|58700003933021546|92700031755124844&gclid=EAIaIQobChMI5duiqem12wIVCySGCh2O3gGoEAQYBCABEgI4LPD_BwE&dclid=CJKM-azptdsCFYyOswodOzcCyw


    What that means is that the distributor was installed incorrectly. It is on the wrong tooth. You will need to remove and reinstall the distributor correctly. I can walk you through it, but it is not an easy thing for someone who has never done this before.
     
  16. ThinRedPaste

    ThinRedPaste Well-Known Member

    that sounds like it's getting into "take it to somebody" territory.
     
  17. ThinRedPaste

    ThinRedPaste Well-Known Member

    what about moving all the plug wires a spot and timing it from there?
     
  18. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    If it sounds like that to you, go with your instincts. If you don't do it right, the engine won't run, and the oil pump won't turn. Maybe there is a member near you that can help. Where do you live?
     
  19. LARRY70GS

    LARRY70GS a.k.a. "THE WIZARD" Staff Member

    That may work! It depends how far out it is. Just keep track of what you do. The distributor rotor turns clockwise. Moving each wire clockwise one spot will retard the timing.
     
  20. ThinRedPaste

    ThinRedPaste Well-Known Member

    I found the bolt and got it loose, but I can't get the distributor to move. I've tried hitting it with my hand, then a screwdriver, then i even tried prying on it and nothing budges it at all.
     

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