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Technical flatty crapping out (exhaust poping) above idle

Discussion in 'The Hokey Ass Message Board' started by david a wright sr., Jan 17, 2018.

  1. 59 flatty 47 model stock eng, new valves springs guides and seats, did it before and after valve job, new points and cond, set at 17, had it set at 12, same thing, been thru dist, working correctly, adv brake adjusted as should be and everything in between, same result,plugs are black, choke eng with hand somewhat better, blocked vac port to power valve(full rich). runs better ie no exhaust firing, backfiring out exhaust, not intake, I did put penney in exhaust crossover in block to keep carb a bit cooler, I read somewhere about exhaust wedges to keep exhaust from leaning out next cylinder, cant find it, any suggestions?
  2. Petejoe
    Joined: Nov 27, 2002
    Posts: 10,407

    from Zoar, Ohio

    Welcome David.
    A few more things. A good condenser is hard to find nowadays. Grab yourself a few more and try them.
    Another look would be changing your coil.
    A blocked power valve is not really a good idea.
    Buy your parts from Max @ Vintage Speed.
    Lots of info here on the H.A.M.B. also on power valves.
    Next. Vac Brake.
    Hook up a meter to your vacuum. Adjust your brake to maximum vacuum, then back it off a few pounds.
    Other than obvious timing and proper plug wire placement this should give you some more garage time.
    Last edited: Jan 17, 2018
    david a wright sr. likes this.
  3. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,589

    V8 Bob

    Clarify "set at 17, had it set at 12".???
  4. I got lucky on mine with the same problem. A carburetor switch out cured it. Never found the exact cause.
    david a wright sr. likes this.
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  5. pitman
    Joined: May 14, 2006
    Posts: 4,858

    from Hampsha

    assumed it's the points setting. (Dwell value, spark behavior)
  6. buffaloracer
    Joined: Aug 22, 2004
    Posts: 792

    from kansas

    I think I'd start with a compression test followed by a leak-down test. I'd also be looking for a vacuum leak.
    david a wright sr. likes this.
  7. jimpopper
    Joined: Feb 3, 2013
    Posts: 92


    Cam with flat lobe or lifter tore up?
    david a wright sr. likes this.
  8. V8 Bob
    Joined: Feb 6, 2007
    Posts: 2,589

    V8 Bob

    Correct dwell for the stock dual point crab is 36 total, and distributor timing should be 10-11.
    david a wright sr. likes this.
  9. point gap
    Joined: Dec 14, 2009
    Posts: 2,229


    Start with fuel pressure and your carb adjustments
    Vacuum readings at idle and off idle?
    Vacuum leaks?
    Coil good?
    Condensers are generally crap now a days
    Is the engine timed correctly?
    Timing advance working?
    Distributor installed and points set correctly?
    Wires on the right cylinders ?
    Right plugs being used?
    Base engine timing correct?
    If all this checks out do a compression test and leak down test.
    Any noise from the engine?
    Broken valve spring?
    Lots it can be, start with the simple stuff first and work your way up.
    Is it 12volt or 6 volt and is your coil addressed accordingly?
  11. Glenn Thoreson
    Joined: Aug 13, 2010
    Posts: 78

    Glenn Thoreson
    from SW Wyoming

    Typical of a flat cam lobe. Did you install new plug wires? Fire it up in the dark and look for cross firing. Check the dist cap for cracks or carbon tracking. A piece of thin sharp metal or carbon in the exhaust passage can set off unburned fuel, also. Firing order correct? Compression good on all holes?
  12. got it fixed, this engine had a oil bath air cleaner originally, and they seemed to always have some restriction, so to check it i cupped hand over carb slightly and she ran correctly, rejetted carb one size larger, numbers gone on my jet drills, and she is doing good, gona watch plugs, might need some more, thanks for all the replys
  13. Petejoe
    Joined: Nov 27, 2002
    Posts: 10,407

    from Zoar, Ohio

    Thanks for the follow up.
    What have you replaced the air cleaner with?
    Some Aftermarket air cleaners are terrible clog hogs.
    doug warren likes this.

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