Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - Holley off idle backfire problem
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Old 05-18-2013, 12:26 PM
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Dont make the mistake of thinking you only have 1 issue. You could have a couple things hurting you. It seem you got the idle and cruise surge cleared up and these are both usually mixture related issues. The backfire on hard acceleration is almost always pump shot related and there is not 1 correct answer. I have fixed a lot of these type issues and it is usually a combination of the correct cam and shooter size.
When you changed the pump cam did you check the linkage to make sure there was no play in it. Most people miss this and it is important. Also when you go over a certain size shooter, the exact size escapes me at this time, you need to also change the shooter screw to the hollow one to allow more fuel.
The proper adjustment of the pump arm is critical. There should be no play between the arm and cam at idle and you need to be sure that at wot there is still some extra room for movement (.015)so you dont bend anything.

I have found the key to carb tuning is to change 1 thing at a time and on things like the pump arm adjustment. Mark it at base line and count turns when adjusting, this will allow you to go back to scratch if need be
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