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Thread: bad surging

  1. #1
    Junior Member JOURNEYMAN
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    bad surging

    In my street car I have a very bad surging problem at all speeds. This started happening after I changed cam and heads a little over a month ago. I know that a bigger solid lift cam will have a little surge to it but I think I have way to much. Even at a cruising speed of 3000 RPM (near 55-60 MPH) the surge is so bad that I am thinking if I do not fix it soon that it will lead to fatigue on the drivetrain. At wide open throttle it runs very strong but it will not level out for cruising at anyspeed. DOes anyone have any ideas what might be causing this? I am out of ideas.

    Thanks, Scott

  2. #2
    im thinking more like your fuel pressure,level,power valve or bad vacume leek been there done that not very fun

  3. #3
    Junior Member SHOW GUEST
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    Quote Originally Posted by corenele
    im thinking more like your fuel pressure,level,power valve or bad vacume leek been there done that not very fun

    I second that!

  4. #4
    Junior Member APPRENTICE
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    My best guess is that your engine is over cammed and not intented for street use/crusing speed. Do you have a mechanical advance in your distributor? If so your weights and springs might not be right for those speeds, might even be broken, also do not use your vacuum advance if so equipped.
    Outside of that, look at your power valve and adjust accordingly. Check your vacuum at idle if you have 8 inches of vaccum at idle put in a 6.5-7.0 power valve. Run 1-1.5 point smaller power valve than actual idle vacuum.
    Action Engineering LLC
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  5. #5
    Senior Member RACING JUNKIE lively's Avatar
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    RABBIT---YOU GOT MORE PICS OF THE CAR IN THE AVATAR!!!!---AND MORE INFO ON IT 8) 8) ---LIVELY

  6. #6
    Senior Member RACING JUNKIE
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    Sounds lean at part throttle to me.

    If you have a power valve, throw it in the trash and put the blocks in place. Jet up 3 sizes and be done with it.
    -WJ Birmingham

    OneBadGMC.com

  7. #7
    Senior Member RACING JUNKIE
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    Quote Originally Posted by OneBadGMC
    Sounds lean at part throttle to me.

    If you have a power valve, throw it in the trash and put the blocks in place. Jet up 3 sizes and be done with it.
    Always thought/was told it was 8 to 10 jet sizes up if you plug power valve. Has worked well for me at 10 sizes up.(secondary pv)

  8. #8
    Quote Originally Posted by Tod74
    Quote Originally Posted by OneBadGMC
    Sounds lean at part throttle to me.

    If you have a power valve, throw it in the trash and put the blocks in place. Jet up 3 sizes and be done with it.
    Always thought/was told it was 8 to 10 jet sizes up if you plug power valve. Has worked well for me at 10 sizes up.(secondary pv)
    power valves are tricky i spoke with pat at pro systems last week and he told me that if changing from a high flow pv to a plug then 10 jet sizes up. if your using a standard pv non high flow then only 6-8 jet sizes and as far as trying to figure out what pv to run in relation to engine vaccum the he also said 2-3 number smaller on the pv then to your vaccum reading at idle hope this all helps.

  9. #9
    Junior Member JOURNEYMAN
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    Thanks to all that have replied. Today I pulled the plugs after driving it for a while and they were tan in color. There are no power valves they were plugged a long time ago. I can not remember what jets are in it but I think I went up about 3 sizes straight from the box. I did not have this issue until I changed cam and heads during the winter so I am guessing the pump to still be good. The float levels haven't changed either. I am using 2- 450 CFM holleys on a Weiand Tunnel Ram Intake (same as before and same dual point distributor as before also. I am just out of ideas.

    Thanks again, Scott

  10. #10
    Senior Member RACING JUNKIE
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    If you changed heads and cam, and it's making more power, you need more fuel to feed it....

    It's lean...

    Another thing that can cause crappy performance at part throttle is the lack of an air cleaner, or air rushing over the top of the carb, throwing the air bleeds outa whack.

    Did you remove the hood? Did you take off the air cleaners? Change anything on the induction side other than cam/heads?
    -WJ Birmingham

    OneBadGMC.com


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