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Holley 750 questions


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I have the 3310 holly vac sec and am having some

issues with it idling the way it should in gear.

The car idles great in park but when I put it in

gear it idles down to 600 rpm. The cam is a 286/

490 comp cam. Well, nedless to say this cam is not

happy at this rpm. Even if I raise the idle in park to 1000 rpm as soon as i put it in gear it

drops to 600 rpm again. I talked to a carb guy and

he suggestedthat I drill a 1/16 hole in each butt-

fly on the primarys. he said this with give the

motor more vaccum and more air at idle so that I

can turn my curb idle down. Has anyone tried this

trick?

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I'll bet when Grumpy wakes up, this can be his coffee and toast editorial. In the mean time I'll take a stab at it. drilling a small hole in the throttle plates is an old trick (to avoid the use of the transistion from idle to open throttle circuits??, it's been a long time on that old trick, and too many cobwebs this time of the morning up there). My first question is what is the stall speed on your torque converter. Have you installed a smaller converter to allow the engine to idle in gear at a higher rpm?

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Your problem is in the covertor stall speed.With my experiences , until you buy a 10" convertor your going to have this problem.My 9" Continental drops from 1050rpm idle to 850rpm in drive. I suggest not drilling the holes in the carb to solve this problems. The holes are drilled for air/ fuel tuneing at idle.

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I also would guess converter. The holes are to increase airflow without increasing fuel flow. It is designed as a crutch for engines with a very large cam. If you need more air, you can adjust the rear throttle blades with a screw that is only accessible with the carb upside down and off the car, but I doubt this is your problem. You can only go so far with the rear throttle blades before they uncover the transition slot and fuel starts to flow through the secondary system. That's when holes are drilled in the throttle blades so they can be closed but still have increased air flow.

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