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Discussion Starter #1
I have an autolite 4100 600cfm carb on a moderately modified 289(302 ported\polished heads, mild comp cam 268 grind,hypereutectic pistons, hipo manifolds\dual exhaust)

The problem is that the car seems to take alot of gas pedal to get moving and sometime stumbles. Once the car is moving everything works great.

I borrowed a 480cfm autolite and there was no problem, no stumbling, and smooth acceleration. We put the 600cfm autolite on a completely stock engine and it worked great.

There is some problem with my engine, and that carb that i can not figure out. Any ideas on what to try next?

keith
 

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I'd suggest vacuum leak, but there are other things to consider: Accelerator pump (can't rule it out, although you did get the carb to work well on a stock motor)? carb linkage (manual tranny with an auto carb)? grit in the carb?
Do you by chance have an aluminum manifold? These sometimes are hard to eliminate vacuum leaks from.

Just some thoughts... Good luck on your trouble shooting.
Daniel
 

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On second thought, it sounds like your fuel pump could be the issue. Don't ask me how I know that. ;)
Daniel
 

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Discussion Starter #4
fuel pump is brand new, but it did come from california mustangs so I cant rule out it being bad. Ive been suspecting the accelerator pump but it did work on a stock motor. I have the stock manifold, and have kind of ruled out a vacuum leak because the 480 cfm worked. The carb is freshly rebuilt and cleaned.
 

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Your assumptions are sound. The carb works great with another motor and another carb worked great on your car. Seems you've centered in on a mismatch between your carb and engine. I would consider rejetting your carb. After the idle circuit the transfer circuit picks up and the carb jets come into play. When you pull your carb apart you'll know the jet size it has and if you knew what size they were in the carb that ran well you could head right for that size. Good luck.
 
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