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Old 06-29-2006, 06:58 PM
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Holes in butterfly's?

Has anyone here drilled small holes in the throttle blades of Holley carbs to lean out rich idling?How has this worked out?What size holes? How many holes in each throttle blade?Thanks!

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Old 06-29-2006, 07:16 PM
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kevan

re holes in butterflys... drill one hole in each primary butterfly close to the shaft[not too close!!!] maximum 3\32
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Old 06-29-2006, 11:14 PM
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I was told to start with .018" holes and go up from there. It doesn't take much unless you have a really hairy cam. The upside is that you have a pretty big window. As long as you're getting enough air to support the idle you need without uncovering the idle transition slots you're fine. If you go too far, you'll just run out of adjustment room in the low end of idle. The blades will fully close and the idle will still be too high. That's a pretty big window. If you go too big, its easy to replace blades and they're not too expensive to buy.
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Old 06-30-2006, 05:54 AM
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carb

There are better ways to fix your problem....


Keith
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Old 06-30-2006, 06:28 AM
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While drilling holes has been a long standing procedure, it really is unneccesary. Holley secondaries have always (at least since the 60s) had a small screw on the secondaries that allow you to bleed in more air so that the primaries will pull a stronger idle signal. it is hard to access with the carb mounted, but is easily visible at the end of the secondary shaft when looking at the carb from the bottom.
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Old 06-30-2006, 07:22 AM
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While drilling holes in the butterflies a carburetor is a standard practice that has been done for years, it is not always necessary or even the proper method of tuning. Yes there are specific applications that would have required this modification on older carburetors, but keep in mind it is extremely hard to “un-drill” a hole once you’ve made it.

Before modifying your carburetor lets go over what exactly you’re working on so you don’t have to spend more money fixing it afterwards
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Old 06-30-2006, 11:35 AM
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Originally Posted by k-star
There are better ways to fix your problem....


Keith
Keith....And those ways would be ...........??????????.............??????????? LOL

Seems to me that opening up the secondaires would give you a real un-balance mixture with half of the cylinders getting a very lean mix and half getting a very rich mix. I dunno, never done it myself, but have drill a few Qjets with excellent results.
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Old 06-30-2006, 11:41 AM
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The changes that would be required will vary depending on why he's having to drill holes in his butterflies. He may not have the secondary butterflies open enough, or may not have enough timing in the engine. He may just have the mixture screws out too far. It could just be a matter of needing to lean out the idle circuits. There isn't a 1 solution fits all.
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