buick 455 running on after shut off????

Discussion in 'Street/strip 400/430/455' started by bad540, May 19, 2020.

  1. bad540

    bad540 Active Member

    my 455 is running on and puffing out the scoops when shut off hot, its driving me crazy everybody has an opinion , but im not sure where to start. it shuts right off in gear? idle is around 850-900 in park 750 in gear, timing is at 31 total it has an 800 qjet. any help would be great as me questions and I can probably help better.
     
  2. hugger

    hugger Well-Known Member

    Crap gas and timing
     
    Max Damage likes this.
  3. LARRY70GS

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

    Lean mixtures and an idle speed that is too high contribute to it. The 72 Buick V8's had an anti dieseling solenoid that would hold the throttle open for curb idle, then close the throttle upon shut down. Buick called it an idle control solenoid.
     
    2dtrak and GSX 554 like this.
  4. hugger

    hugger Well-Known Member

    Nozzle drip too
     
  5. knucklebusted

    knucklebusted Well-Known Member

    I agree, too much timing and/or bad gas.

    There are a few things you can do to tweak down.

    First, do you have vacuum advance hooked up? If so, I'd hook it to manifold and not ported. If you have to readjust the idle on manifold vaccum it should help it shut off.

    Second, maybe swap one of the light springs for the next one up to keep advance from coming in too low.

    Last, lower the idle a 100 RPM if possible and tune your idle with a vacuum gauge to get it optimal.

    Later cars came with a solenoid that would drop the idle back when powered off to help avoid that.
     
  6. LARRY70GS

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

    Yup, too much throttle opening.
     
  7. GSX 554

    GSX 554 Gold Level Contributor

    Larry is correct . Idle too high .
     
  8. hugger

    hugger Well-Known Member

    High idle speed by itself generally isn't an issue,..gotta remember alot of us with large cams run upwards of 1300 rpm idle,..now granted it's done more with high initial advance and idle mixture,..and not just cranking the primary doors open,...but nonetheless,..

    A 900rpm free idle is normal,..as Larry mentioned the amount of the opening used to obtain that speed can be one of or the sole issue
     
  9. hugger

    hugger Well-Known Member

    A high float setting or non sealing needle will cause drip,..coupled with a hot intake and combustion chamber = run on
     
  10. telriv

    telriv Founders Club Member

    As you stated no problem when shut off in gear. Get used to doing that & you will be fine. Just remember to put it back in park when done. If ALL your linkage is hooked up properly & functioning properly as it should you should not be able to turn the ignition switch off UNLESS it's in park.
    The too fast idle speed in park/neutral is normally the ultimate culprit.
     
  11. GSX 554

    GSX 554 Gold Level Contributor

    Bring down the idle speed in drive by 50-100 RPM and you will probably cure your problem . I'm sure your talking about a stock and not some big cammed monster .
     
  12. bad540

    bad540 Active Member

    more or less a stock set up kenne bell hydralic cam mild combo . I am going to focus on the idle mixture and the idle speed the screw is turned in quite a bit to get that idle so the doors are probably opened to much at shut off makes sense. quick story that may help , pertronics ign . sucks fought with the car leaving me places and not starting and back firing at will, they said it either runs or it doesn't that isn't true it ran, but fought with it for a half of summer. they would not stand behind there products . so tore it out put an msd 6al in it with points firing it, car was completely different had to turn the idle way down ran sooooo much better everywhere, and is so smooth and nice now. ran the best et to date , 13.02@ 102 4200lbs but I MESSED with so much stuff trying to work around a bad ign system.i paid good money to find and old school distributer guy and set that distributer up to the letter but I changed a lot with the ign problem and I don't remember where it was . and the man has now passed and cant get it back where it was. you guys on here are great and helpful thanks again. don't buy pertronics products...…..
     
    Last edited by a moderator: May 20, 2020
  13. LARRY70GS

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

    The more ignition timing you have at idle, the less throttle opening you need to idle at a specific RPM. You can't run whatever timing you want at idle, it depends on the distributor you have, and how much mechanical advance THAT distributor has. They are all different. You probably don't have enough timing at idle. That's why you have to open the throttle more than you want.
     
    Last edited: May 19, 2020
  14. hugger

    hugger Well-Known Member

    Yep I try to have at least 18° initial myself,...most the time 22 to 24
     
  15. chrisg

    chrisg Silver Level contributor

    High operating temperatures can also cause this. Do you know what the coolant temperature is when you are seeing this problem?
     
  16. Mark Demko

    Mark Demko Well-Known Member

    X2, being your only at 31 total, add about 3 degrees more initial for a total of 34.
    The additional timing at idle will allow you to reduce your throttle opening a bit which may eliminate your run on issue.
     
  17. Raymond levesque

    Raymond levesque Raymond Levesque

    If im hearing the exhaust tone change just above idle, whats causing that? Im thinking the re mfg distributor. Mechanical advance is not working correctly...
    I have a 69 400 with a Quadra jet carb and the book says to set the timing to 0. It dont like zero.
    Sometimes it idles fast, sometimes almost stalls.
     
  18. knucklebusted

    knucklebusted Well-Known Member

    Factory timing in this day and age is out the window. You need to recurve the distributor if you haven't already and you need to power time it. I would never set my timing to zero. Larry's power timing thread is the one you need to look into. Try at least an initial timing of 10° and adjust mixture and throttle to suit then continue from there.
     
  19. LARRY70GS

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

    Ignition timing is one of the most misunderstood topics discussed here. I wrote this thread to try and help,

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

    The book says 0 because the original distributor part number 1111335 had the following specs,
    1969DistSpecs.jpg
    That distributor had a maximum mechanical advance of 30-34*, so 0* (TDC) makes sense. Once you change the distributor, the book specs go right out the window, they no longer apply. Initial timing is just that, initial. Once you step on the gas and engine RPM climbs, ignition timing changes. Mechanical and vacuum advance add timing. The 1969 engines used manifold vacuum to run the vacuum advance. That means the vacuum advance would add timing even at idle. No engine will like to idle at 0*. Not only will it not like to idle there, but if you run it there, the engine will want to run hot or overheat. If the engine has a cam, you'll be lucky if it idles there at all.

    Using a timing light, and light springs, it is easy to see what you timing will be, and to verify that the mechanical and vacuum advance systems are working, and to measure how much advance they add. The various distributors used over the years in Buick engines are NOT all the same. The amount of mechanical advance built into them varied greatly depending on which distributor part number you have.

    Let's start there, what is the part number on your distributor? It is stamped into the body just under where the cap sits.
     
  20. BQUICK

    BQUICK Gold Level Contributor

    Carbon buildup...….SeaFoam it
     

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