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I have a 67 mustang with a 302. (Holley 4160 600cfm carb, edelbrock air gap intake, edelbrock performer plus cam, port matched iron heads, long tube headers, faul flowmasters) my problem is I had a 600cfm holley 4010 on it whose float started taking on fuel the day before cruisin' the coast last year, ran great on that carb. Swapped out carbs and tuned my idle air circuit with vacuum gauge and all. Car runs pretty good except higher rpm at part throttle. If you are half throttle at around 3k or higher it starts to stutter and pop a bit but if you floor it it pulls good with no hesitation. I have an accel points eliminator installed and timing at around 12 degrees btdc. I've tried going up and down a squirter size, tried several different secondary springs. I cannot seem to figure it out. Any advice?

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If fiddling with the accelerator pump didn't work it sounds like you need to make the idle/transition circuit and/or the main circuit richer.

Because it is easy, I would simply turn the idle mixture screws out 1/2 a turn and see if it has any effect.

The next easiest thing to do is to put some small diameter wire in the air bleeds. Do the idle bleeds first and if it has no effect or a negative effect try the main bleeds. The point here is to try and figure out which circuit is the problem.

If you think the issue is with the main circuit the next step would be to up the main jet and or use a higher number power valve.

If you think the issue is with the idle circuit you may need to enlarge the ifr slightly to resolve it.

A wideband O2 meter makes this process a lot easier.
 
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