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Truck not able to low idle Carb?, Timing?

Discussion in 'Chevy Trucks' started by steven1213, Mar 31, 2008.

  1. steven1213

    steven1213 Junior Member
    Messages: 20

    I installed a 1981 350 engine in my '76 truck and when I got it to fire up I am unable to get it to idle low. If I open up the choke on top of the carb I can get it to idle fast. once it gets up to operating temperature and I rev up the accelerator quickly to get the carb to reset to low idle it just dies. The only way to get it to idle is by turning up the fast idle screw to where the truck is idling really high. Once I bring the idle down a bit the motor motor dies out when I hit the throttle. If it dies, it is hell trying to get it to start again, at times to the point of priming the carb with some gas to fire it up. I did set the timing with the vacuum advance tube plugged but the idle needed to be high to do it. I heard it could be that the pump in the carb may be bad which would cause it to die when giving it gas. Also the motor backfires out the carb at times when quickly pressing the accelerator when the idle is lowered. Any help in this matter would be appreciated. The carb is a quadrajet with the spring type choke that mounts on the intake manifold. ------------------------Steve
     
  2. scottL

    scottL PlowSite.com Addict
    Messages: 1,603

    Was the carb rebuilt clean just before putting it on this new engine? or was it the old carb. Typically a few back fires through the carb could fault the carp functioning properly. Otherwise, carb, timing, vacum.
     
  3. Cooter24

    Cooter24 Senior Member
    from NE Iowa
    Messages: 268

    Double check and make sure you have the correct firing order. Then proceed with the carb, timing and vacum.
     
  4. steven1213

    steven1213 Junior Member
    Messages: 20

    Cleaned the carb and reinstalled

    I took the carburetor apart and and cleaned it. After I reinstalled it, it ran much better and no backfiring.The fuel filter needed changing and the float level was not adjusted correctly. We also found that the vacuum choke brake control is no good. The only problem I am having now is I am unable to get it to idle at a normal speed consistently since we replaced the fast idle cam (part with the steps) and it seems to catch the throttle to where it does not touch the fast idle screw on the other side of the carburetor. This causes it to not go down to normal idle speed after warming up to normal operating temp. The fast idle cam is the same as the old one but not as worn and has sharper edges on the steps. could this be a matter of just adjusting the fast idle cam screw? The carb no longer backfires and works great other than that and the tendedncy to load up and die when you first warm it up if you start it and leave it unattended. The firing order and vacuum lines are all correct. Thanks for any advice.----Steve
     
  5. scottL

    scottL PlowSite.com Addict
    Messages: 1,603

  6. steven1213

    steven1213 Junior Member
    Messages: 20

    It turns out the carb needed a vacuum choke brake. The plunger on the old one was bad. It starts up and runs much better at a high idle to warm up instead of loading up and fouling the plugs on initial warm up. Had to order it from a parts place 1400 miles away since they don't make them any more. Well worth it though instead of spending 280 bucks on a new carb.