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High idle & running rough

Discussion in 'The Hokey Ass Message Board' started by mack57, Jul 28, 2013.

  1. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    Hey all,
    '48 chevy coupe w/305/350. Runs erratically... When outside temp is hot it runs beautiful and strong, when cool starts to high idle & rough when in gear. I was thinking vacc leak? It seems to run differently on it's own whim.... Stumped & frustrated.
    What are your thoughts?


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  2. George/Maine
    Joined: Jan 6, 2011
    Posts: 949

    George/Maine
    Member

    If you have a quad jet carb the toddle shaft could be worn. high idle then low and stall.
     
  3. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    Recently updated from Q-Jet to edelbrock with elec choke.


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  4. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    If it started right after the carb swap, then its the carb. My sons was doing that.....

    Could even be a stuck advance plate/broken spring in distributor
     

  5. 68vette
    Joined: Jul 28, 2009
    Posts: 306

    68vette

    I think you recently DOWNGRADED from Q-jet to edelbrock...

    Sounds like the problem is in the choke portion...good luck.
     
  6. Devin
    Joined: Dec 28, 2004
    Posts: 2,352

    Devin
    Member
    from Napa, CA

    I recently had some carb woes with an edelbrock. Aside from tuning, I would bet money they there's some sediment and other crap in the carb. Yes, even a new carb.
     
  7. Devin
    Joined: Dec 28, 2004
    Posts: 2,352

    Devin
    Member
    from Napa, CA

    Actuall, I must retract my post after re reading the OP. not sure if sediment would cause this problem.
     
  8. oj
    Joined: Jul 27, 2008
    Posts: 6,257

    oj
    Member

    I bet the problem is in the design difference. The intake is for the quadrajet, right? with those huge holes in the secondaries. The edelbrock will bolt up but you can have a vacuum leak at the rear because it is squarebore. Unless you bought a q-jet replacement type edelbrock, then they are the same as quadrajet.
    Edelbrock sells a flat plate that seals that area off or you can add a spacer to seal it off.
     
  9. henry29
    Joined: Sep 5, 2007
    Posts: 2,835

    henry29
    Member

    What adapter did you use and which gaskets?
     
  10. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    It is an edelbrock intake mated to the carb, Correct gasket.

    The trans crossmember was just replaced and trans tail us approx 2" higher now. Carb was installed " out of box" and ran great before tranny lifted.

    It then ran good at idle but, when put into gear it bogged badly. Pulled plugs and replaced with fresh, ran great again.... Now, starts to a very high idle.... It's crazy?!?


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  11. Bigchuck
    Joined: Oct 23, 2007
    Posts: 1,141

    Bigchuck
    Member
    from Austin, TX

    Eletric choke sticking? Fast idle cam?
     
  12. SMOG_GUY
    Joined: Jun 28, 2011
    Posts: 388

    SMOG_GUY
    Member
    from Dinuba

    High idle always makes me think vacuum leak.
     
  13. dtracy
    Joined: May 8, 2012
    Posts: 223

    dtracy
    Member

    Is the vacuum line off the modulator if automatic?

    Dave.
     
  14. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    Hi Dave,
    It's attached. Would a leak in that line be a cause?


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  15. PackardV8
    Joined: Jun 7, 2007
    Posts: 890

    PackardV8
    Member

    Put an angle gauge/inclinometer on the intake manifold carb mounting surface and get back to us with a reading.

    When the engine installed angle was changed, the carb float level was changed also.

    jack vines
     
  16. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    -4.5


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  17. mustang6147
    Joined: Feb 26, 2010
    Posts: 1,847

    mustang6147
    Member
    from Kent, Ohio

    A weak ignition will also act this way.... If you lifted the engine, and perhaps a wire got pinched? WHo knows.... Put the old carb back on and see if it acts the same....
     
  18. bgaro
    Joined: Sep 3, 2010
    Posts: 1,189

    bgaro
    Member

    try it with out the choke, see what happens. at least you could rule this out.
     
  19. Larry T
    Joined: Nov 24, 2004
    Posts: 7,661

    Larry T
    Member

    A square bore Edelbrock on an Edelbrock intake for a spread bore (Quadrajet) carb can still have a vacuum leak on the secondary throttle bore.

    You have to use a metal plate sandwiched between 2 gaskets or an adaptor.
     
  20. guitard
    Joined: May 16, 2012
    Posts: 198

    guitard
    Member

    I'm betting vacuum leak. If no lines are cracked or off, squirt around the base gasket.
     
  21. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    Larry T,
    Thank you! I'll check it out.


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  22. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,911

    brokenspoke
    Member

    ^^^^^^what he said....I experienced the same thing
     
  23. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    Brokenspoke,
    What are you driving? Is it a '48? I can't see the pic well....


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  24. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,911

    brokenspoke
    Member

    Yes its a 48 Ford
     
  25. mack57
    Joined: Apr 17, 2013
    Posts: 176

    mack57
    Member

    ImageUploadedByH.A.M.B.1375142137.888694.jpg


    This is the manifold I'm using with the edelbrock carb. Looks like a match....

    Car started & ran great today... No vacc leaks found yet. Checked around the carb, manifold to heads, lines.


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  26. brokenspoke
    Joined: Jul 26, 2005
    Posts: 2,911

    brokenspoke
    Member

    ....You will most likely need a adapter/spacer plate....
     
  27. 68vette
    Joined: Jul 28, 2009
    Posts: 306

    68vette

    Usually you have a whisle sound with a vac leak....I just found one on my car after a carb rebuild....I used the only carb gasket that came with the rebuild kit....found the leak by spraying brake cleaner around the base of the carb as that was where the sound was coming from....yep...it was the new gasket....wrong one for my car....last Hygrade made by standard for me.

    Forgot to say, the engine speeded up when I sprayed on the leaking area.
     

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