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Old 12-13-2008, 11:45 PM
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sbc stumble and back fire

i built a 355 for my 1995 c1500 that is bagged. the motor is zero decked forged flat tops alum heads proformer rpm air gap dule plane intake roller rockers 280h comp cam egale rods and crank balanced balencer to fly wheel abou 10.1:1 compreson 650 double pumper carb msd pro bilit hei hole shot 2400 700r4 3:42 gears for now im haveing a stumble off ideal if i stab the trottel its got a bad hesatation but if i come up on it easy its fine and if i come up above 2500 rpms and stab it its fine ive tryed messing with the timeing but no diff also runing down the highway at high rpms and let out it back fiers real bad the timeing is 34 deg total i cant remember what the in is any other specs just ask ill try to remember oh and any est on hp the heads are 195 intake 2.02 1.60 valves

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Old 12-14-2008, 09:19 AM
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The stumble is most like from the carb. to much fuel are to little when you hit the skinny peddle. I would guese to much fuel is being duped in be for the engine can use it all. there are cams the change the amount of fuel the accelerator pumps dump in the engine i would start with the secondaries first.

Skeeter
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Old 12-17-2008, 03:40 PM
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ive moved both primaries and secondarys that didnt help i tried with the cams off to see if it would help with no squirters but it made it worse the truck runs rich at idle?
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Old 12-25-2008, 03:40 PM
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backfire

If it is worse when it gets warm it might be the module in the distributer. there about 25.00 at auto parts. worth a try before tearing into a carb unless you know it needs a rebuild anyway.I always thought backfire in carb is electrical and exhaust backfire is carb?
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Old 12-25-2008, 05:12 PM
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Make sure that you have no slack in the accelerator pump mechanism first. Go back through the basic tuning procedure of a Holley, 1-1/2 turns on the idle mixture screws so on ans so forth......

Then......, if that's not the problem.

Try bumping the initial timing up until it quits. Take a reading on total timing after you get the stumble fixed to see where it is. If you have an HEI distributor you'll have to make a few mods to limit the amount mechanical advance. If it's an MSD, install the bushing that limits your total timing close to, or less than, 36 degrees.



Larry
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