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235 stumbles off idle. VIDEO enclosed.

Discussion in 'The Hokey Ass Message Board' started by Scott F., Jun 17, 2012.

  1. Scott F.
    Joined: Aug 9, 2006
    Posts: 969

    Scott F.

    See the video. Provide input please. Just put a new coil, condenser and points on. Dwell at 40 degrees (probably a bit high but couldn't find specs). It's a '54 235 in a 54 chevy.
  2. Scott F.
    Joined: Aug 9, 2006
    Posts: 969

    Scott F.

    Darn video didn't attach. Here's a description: When running normally and you 'stab' the throttle it falls flat, seems to really suck air for a second, and then comes up on RPM's. (this is in neutral but in gear, running around, it is the same). A steady, slow increase of the throttle results in a slow, steady increase in RPM's. Thoughts?


  3. Scott F.
    Joined: Aug 9, 2006
    Posts: 969

    Scott F.

  4. accelerater pump in the carb,may not supply enough gas.

  5. Scott F.
    Joined: Aug 9, 2006
    Posts: 969

    Scott F.

    You guys probably can't see this video. I'm not sure how to make it so you can see it. I tried putting it up direct on here but it was rejected.

  6. Try putting the video on You tube .

    My truck had that stumble off idle for ages, fine tuning the timing / idle mixture / valve lash / plug gaps all helped.

    I pulled the carb, cleaned and cleaned it , put a kit in , did all of the above again . got it a little better .

    Tossed the carb (W-1) and fitted an old Zenith outta the junk heap in the shed ...... Goes Bloody Brilliant !!!
  7. canadianal
    Joined: May 15, 2012
    Posts: 164

    from canada

    make shure your accelerator pump squirt comes in as soon as possible off idle if you have to adjust do so it may be getting air before fuel and going lean for a second
  8. Nailhead Jeff
    Joined: Jun 13, 2009
    Posts: 120

    Nailhead Jeff
    from fresno

    If you have a Rochester carb check the accelarator pump link hole. I've seen them wear so bad that the pump doesnt squirt till about 1/4 throttle.
  9. greaseguns
    Joined: Dec 24, 2006
    Posts: 135


    bump your timing up dont go by the bb in the flywheel advance it enough to take out the stumble and not ping wont take much . 28 to 35 deg dwell new points .019 and used .016
  10. UPSrodder
    Joined: Jun 9, 2005
    Posts: 566


    had a terrible stumble with mine. Advanced the timing and bingo. I used a vacuum gauge to set it up pull as much vacuum as you can at idle and you will be good.
  11. Road Runner
    Joined: Feb 7, 2007
    Posts: 1,257

    Road Runner

    I had a Rochester B carb once that had the same symptoms.
    The accelerator pump spring was too small/weak and squirted too much gas.
    Replaced it with a longer spring from a spare carb and problem was solved.

    The RochB accelerator valve is vacuum operated, so the spring (or springs with more than one carb) needs to match the engine to work properly at part or wide open throttle.
    If the spring is too weak it will open too wide, too soon and flood the intake, giving too rich gas mixture and the engine hesitates/stumbles until it can recover.

    Check the timing and carb idle mix settings first, also check for vacuum leaks at the intake and vacuum advance and then check the carb.
  12. Snarl
    Joined: Feb 16, 2007
    Posts: 1,639


    Sounds like the accelerator pump isn't working. Take the air cleaner off and look inside the carb with it running. Goose the throttle and see if it squirts a stream of gas into the carb or not.
  13. cederholm
    Joined: May 6, 2006
    Posts: 1,621


    This and cleaning my accelerator pump worked on my '53 235. Same problem.
  14. Big T
    Joined: Aug 29, 2006
    Posts: 638

    Big T
    from Florida

    Carb rebuild (W2) and addressing accelerator pump worked on my '53 235.
  15. xderelict
    Joined: Jul 30, 2006
    Posts: 2,477

    Member Emeritus

    I've been dealing with the same issue on a GMC engine and after going thru about everything the fuel pump was not working right. Crack the fuel line at the carburetor and turn it over to see if you have fuel at the carb.Mine didn't, quick change out and it's running much better.

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