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Thread: carb stumble???

  1. #1
    Senior Member MASTER BUILDER
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    carb stumble???

    I recently changed the carb and intake on my sbc (350 .60 over .510 lift cam 292 duration,edelbrock rpm heads 10.5-1 comp. victor jr intake 750 dp) now when I feather the accelerator to take off (4 spd) it has a slight dead spot and it has a low speed miss?? But as soon as I get past that spot in the accelerator pedal it clears right up. I was planing on going to the track sat. for test and tune, and was wondering what I should be looking for to cure this problem, I already played with the accelerator pump adjustment and checked the floats, and low speed mixers. thanks in advance.

  2. #2
    Senior Member RACING JUNKIE fla1976's Avatar
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    stumble

    Have you read your plugs. Sounds like you need to rejet the carb.

  3. #3
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    no I have not read the plugs. I havent had it to the track yet or any place I could wind it up and shut it down . any other suggestions.

  4. #4
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    any idea what size jets I should be running with this combination?? I havent pulled the bowls off to see yet.

  5. #5
    Senior Member RACING JUNKIE fla1976's Avatar
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    jeys

    I'd pull the bowls and see what it has. Then, I'd jump the size a couple and retry it.

  6. #6
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    the fronts are 66 the rear is 72H does this sound right??

  7. #7
    Senior Member RACING JUNKIE
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    Quote Originally Posted by whitey70ss
    the fronts are 66 the rear is 72H does this sound right??
    What is the model number? That looks too lean for a 750.

    4779 came with 75/76 and 8.5 PV
    4779-1 came with 70/80 and 8.5 PV
    4779-2 came with 70/80 and 6.5 PV
    4779-3 came with 70/73 and 6.5 PV
    4779-4 came with 70/80 and 6.5 PV
    4779-5 came with 70/80 and 6.5 PV (same as the dash 4)
    4779-6 came with 71/80 and 6.5 PV
    84779 came with 70/73 and 6.5 PV

    There are also some other OEM and marine part numbers.

    Dave
    Dave
    http://www.racingjunk.com/profile/343797
    "All that is necessary for the triump of evil is for good men to do nothing" Edmund Burke

  8. #8
    Senior Member MASTER BUILDER
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    I drove to the (local)speed shop today and talked to a guy that teaches a hi-po class at the local college. he told me I needed a 45 power valve I had a 65 and told me to jet it 72 in the fronts and 80 in the rears. I put it together and now its raining :cry: it does seem to have better throttle response now :roll: I guess I'll see sat.

  9. #9
    Senior Member RACING JUNKIE
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    That's a pretty big jet spread. Rear cylinders are going to get more fuel than the front.

    Last I heard (haven't run carbs in a long time), 4 jets were the biggest spread you want to do from front to rear.

    Maybe someone with better carb knowledge can comment on that.
    -WJ Birmingham

    OneBadGMC.com

  10. #10
    Senior Member RACING JUNKIE fla1976's Avatar
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    Jets

    I always tried to run mine square. All four the same. I guess there is no real reason except that it was race only.

  11. Racing Junk


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