Q-jet expert question

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Sparky, Sep 27, 2001.

  1. Sparky

    Sparky 1/2 ton status

    Aug 20, 2000
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    San Antonio(summer) Texas A and M (school year)
    I rebuilt my q-jet six months back and evrything has been perfect untill recently. I think the plugs (forget their proper name) that seal the float bowl are leaking. You know the ones that are suposed to get epoxy when you rebuild the carb. Here are my symptoms:

    1. It has become hard to start when it sits overnight. It always starts righy away but then dies on me like the float bowl has no gas. On the second try it picks itself up and runs fine.

    2. Gas mileage has gotten 1-2 miles/gallon worse, and it smells like gas. After I rebuilt it I was passing emission testing for new cars without haveing cats and smelled like normal exaust should. I think it leaks while I am driveing causing a rich mixture and bad gas mileagae.

    Here is my question... Does it sound like the epoxy wore off and is causing the described problem? And, Can I reapply the epoxy without haveing to totaly rebuild the carb again? If I recall right, you can take the carb off the truck and get to them without haveing to dismantel the carb. I had access to an exaust analyzer when i tuned it and would like to not mess the mixture screws and evrything if I dont have to. What kind of epoxy should I use when i fix the problem? Last time I just used whatever was laying in my friends dad's shop. If this does not make any sense, let me know and I will try to clarify. Thanks


    When all else fails... Check the blinker fluid.
    78 K-5
  2. Blazer1970

    Blazer1970 1/2 ton status

    Feb 17, 2000
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    Old Mission, MI
    It may be the plugs leaking. Easy to check, you can remove the throttle plate from the bottom of the carb without disassembling anything else. Remove the two screws visible on the bottom of the carb, and the two long screws that go down from the top at the back of the carb. It is also possible that your power piston is stuck in the "up" position, although that would not really tie in with it being hard to start in the morning. You can check the action of the power piston by sticking something (I use a small allen wrench) down through the bowl vent tube that sticks up just in front of the primary bores.


    70 Blazer CST 4X4 350 SM465 NP205
    87 Burb 4X4 350
    01 GMC 2500HD 4X4 Duramax/Allison
  3. dyeager535

    dyeager535 1 ton status Premium Member

    Dec 13, 2000
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    Roy WA
    Remove the air cleaner. With truck cold, (and off) depress accelerator pump a couple of times. Each time you should get strong squirts of gas into the primary. If you don't, the float bowl is empty. Usually leaky well plugs are the cause if its been sitting for a bit.

    You could start truck, and then shut it off, and test again. Float bowl should be filled by now (if everything is working correctly) and when you depress the accelerator pump, you should see the gas shooting into the primaries again.

    I think I'd check choke. Start then stall, I'd guess either choke or vacuum, since you have fuel obviously, or it wouldn't start in the first place. My experience with a decent vacuum leak is start, stall, start, but constantly rough idle. It will ALWAYS be rough at lower RPM's.

    Bad mileage could very well be the choke adjusted slightly incorrectly.

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