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Author Topic:   holley 4412
posted March 31, 2003 04:13 PM
I bought a after market rebuilt carb it was supposed to setup for my engine combination. When we run this carb the carb would hesitate before going wide open once it was wide open there would be no problem. Jets were changed from 71 to 75 no difference. We changed everything heads three differnet distributors cams everything we could think of finally as last result we changed the carb with one that a budy had engine worked good not a problem . We changed the acc pump thinking that may be the problem . Installded back on same problem this happened at various points on the track. could the cam that was put on the carb be wrong any sujesting would be helpful or should use this carb as a boat ancor.

posted March 31, 2003 04:30 PM
Alltel is exactly right- you want the lever on the pump body to be making light but definite contact with thescrew on the pump arm. That way, the pump will be actuated the instant the throttle shaft starts to rotate.

The above will help if the problem occurs when you first apply the throttle. If the problem occurs later- somewhere around corner exit- then you probably have a power valve installed that opens too late- like a 2.5 or 3.5. If that's the case, attach a manifold vacuum gauge to the tube beneath the fuel bowl and see what your vacuum is at idle. Then install a power valve that opens at 1.5 to 2.0 in. below that figure. For example, if you have 10 in. of vacuum at idle, try an 8.5 power valve; if you have 8.5 in. of vacuum at idle, try a 6.5 power valve. If you don't have a vacuum gauge, then install a 6.5 power valve and see if the problem goes away. I would recommend using a vacuum gauge if at all possible. Don't forget to zero it out before using it.

Let us know if the above doesn't help and don't worry, the carburetor is definitely fixable.

Earl Parker II

[This message has been edited by Earl Parker II (edited March 31, 2003).]

[This message has been edited by Earl Parker II (edited March 31, 2003).]

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