Carb question

Discussion in 'Engine Topic' started by Layne02, Nov 25, 2017.

  1. Layne02

    Layne02 Member

    81
    1
    Jun 25, 2013
    Georgia
    Hi everyone. This question is not about my Camaro, it is about a Gmc truck I am restoring for my son. I rebuilt the 305 recently and it has been running great . Then , yesterday I put a different throttle return spring kit on it. After that it started running really rough , even stalled a time or two. Now to put this spring kit on, I had to keep throttle pushed back the whole time, which had choke plate open , so I am wondering if I allowed some trash in.

    It is running better after letting it run some and adjusting idle screw, but, still not right. I used temp gun on exhaust ports while it was hot and numbers 3 and 5 were not nearly as hot as rest, so if trash got in, would it cause a mis in 2 cylinders ? I'm not sure what else could have went wrong so fast , if all I did was put spring kit on, any thoughts?
     
  2. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    8,873
    142
    Nov 4, 2004
    Ringgold, GA
    Well I don't think I've ever heard of replacing a return spring causing the engine to run rough. You may have bumped a vacuum line off or something of that nature. Likely going to be something simple, you just have to find it. Good luck.
     
  3. Layne02

    Layne02 Member

    81
    1
    Jun 25, 2013
    Georgia
    Vacuum lines are fine, I guess what I am getting at is 2 cylinders are suddenly missing , would trash in carb cause that?
     
  4. CorkyE

    CorkyE Veteran Member Lifetime Gold Member

    8,873
    142
    Nov 4, 2004
    Ringgold, GA
    Not likely that trash in the carburetor will cause a miss on 2 specific cylinders. Are the plug wires is good shape, not trace arcing? You can check this at night time, you would be surprised at the light show worn out wires will put on. Off to church for now.
     
  5. Layne02

    Layne02 Member

    81
    1
    Jun 25, 2013
    Georgia
    Ok , figured it out, the 3 and spark plugs were not firing good, replaced them and its back to running great.
     
  6. 1980RS

    1980RS Veteran Member

    1,595
    12
    Jun 17, 2006
    It is possible that the throttle shaft is worn out, so when you put the stiffer spring on it the it pulls the throttle at an angle so one blade is more open that the other. I have had this happen on Q-jets.
     
  7. cadillac_al

    cadillac_al Veteran Member

    526
    33
    Apr 22, 2015
    Maine
    Qjets wear the bushings because GM put the spring at the rear of the throttle shaft. The spring should be moved to the front of the throttle shaft to even out the pressure and lessen the wear. Just one of my pet peeves since we are talking about throttle springs.
     

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