I have a holley carb, 750cfm vaccum secondaries. Stock 396 with malaroy unlite distributor, and acel coil. Recently my mixture screws have become useless, they use to change the engine and the way it ran, doesn't do that any more. Anybody got an idea of what the problem could be?
Thanks in advance. http://www.chevelles.com/forum/biggrin.gif

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One problem could be the jets are too big. I've noticed this before experimenting on jet sizes.

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Mike Hurta
(Aug98)
Gold#25
Clute, Texas
www.chevelles.com/feature/aug98.html (http://www.chevelles.com/feature/aug98.html)

Vacuum leaks can render them useless, also.

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Pat Kelley
66 El Camino, daily driver
67 El Camino, STRIP/street

It has the stock jets which at one time were fine, and I just rebuilt to try and remedy this problem but it is still the same.

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Drilling SMALL holes in the primary butterflies will provide more idle air, and the idle mixture screws will have effect. If you don't know what i'm talking about, get a holley book.

Basically, at your idle setting, you have probably opened the throttle enough that the idle transfer slot is fully exposed, rendering the idle mixture screws useless. You are idling on your main circuit.

Drilling small holes in the primary butterflies will allow you to back off the idle screw. Leave about 0.040" of the slot exposed below the butterflies.

Start small or you'll be soldering them shut!

Email me if you need more help.

RH

Charles,
Do NOT drill any holes in your carburetor! If the carb was working fine before and only now with time it is experiencing problems, drilling holes in it will not fix it. Here is a very simple solution for you to try right now. Looking down in the primary butterflies you will see 4 small holes on the leading edge (side closest to the floats). Get a new can of carb cleaner with the plastic straw type extension-put the end of this straw directly into each of those four holes and spray for at least 3-5 seconds. This will clear out any junk or carbon that may be lodged in the small passages of the idle circuit. If you rebuilt the carb correctly doint this procedure will clean out the idle circuits and you should be back in business.
If the car will idle, you should do this procedure with the motor running. If the car will not idle and you do this with the engine off, it may take a moment or two of cranking to get the engine to start. A good setting for idle mixture screws (baseline) is 1.5 turns out from fully seated. Hope this helps.

I would check to be sure thereis not a blown power valve,a backfire can cause this. John

i had the same problem with a holley 2300. i also noticed that looking down the venturi while idleing there was fuel dripping. the problem was dirty-clogged air bleeds. i agree with go69 try the spray. if the spray doesn't work and you feel confident that you can dissasemble, clean, and reassemble with new gaskets napa sells carb cleaner for about $10 a gallon. it works very well. use caution with this stuff. worked for me.

Thank you i cleaned out the four holes you suggested Go69 and it got better, thanks again. :d

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