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Old 07-01-2005, 05:16 PM   #1 (permalink)
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Unresponsive Holley idle mixture screws...

Why might the idle mixture screws on a Holley carb be unresponsive? Open them them way far and it roughens up a little. There is a very slight difference between fully closed and 1/2 turn open, but it does not die or run very rough as it should. Idle throttle opening screw is opened only slightly and it's a stock motor, so I doubt if the throttle blades are open too far. Car runs and drives pretty well, but it smells a tad bit rich. Thoughts?
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Old 07-01-2005, 05:20 PM   #2 (permalink)
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Unresponsive Holley idle mixture screws...

Sounds like the float level is too high. Possibly rear throttle plates partway open, although that usaully is that way because someone set them that way to get more air in the idle mixture for a real steep cam and no vacuum at idle.
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Old 07-01-2005, 05:22 PM   #3 (permalink)
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Unresponsive Holley idle mixture screws...

what idle rpm? screws dont react over 900 rpm. usually 1 1/2 turns out is ballpark. dirt in the airbleeds at the top of the venturi can cause problems.
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Old 07-01-2005, 05:36 PM   #4 (permalink)
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Unresponsive Holley idle mixture screws...

~600 RPM. I'll take the thing apart and check to be sure it's clean then set everything from scratch. Probably best to do it that way anyhow, to be sure everything is right and not be throwing guesses at it. Thanks for the tips.

This carb has sat for a while (though it was drained of fuel) so it could just need to be cleaned up.
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Old 07-01-2005, 08:32 PM   #5 (permalink)
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Unresponsive Holley idle mixture screws...

Whenever I have found this condition and the idle/floats are set correctly, it's the metering block gasket. If you take it apart be sure to put new gaskets between the throttle body and the metering blocks. Should clear it up.

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Old 07-01-2005, 09:06 PM   #6 (permalink)
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Unresponsive Holley idle mixture screws...

you might also check the idle mixture screws themselves, they can get worn where they're supposed to seal, this could cause it not to kill the engine when ran all the way in.
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Old 07-01-2005, 09:23 PM   #7 (permalink)
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Unresponsive Holley idle mixture screws...

Thanks for the tips guys. I'll definitely put new gaskets in it and check out the neddles of the idle mixture screws. I'm betting it's just leaking internally from gaskets dried up. I think they are cork gaskets (IIRC from looking at it earlier) not the new reusable blue type.
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Old 07-01-2005, 09:23 PM   #8 (permalink)
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Unresponsive Holley idle mixture screws...

I just pull 'em out & spray carb cleaner in them until cleaner comes out the bleeds
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Old 07-02-2005, 12:07 AM   #9 (permalink)
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Unresponsive Holley idle mixture screws...

Failing all those things, it could be a leaking power valve. Or if you have low idle vacuum, it could cause the PV to open slightly - making it run rich and impossible to shutdown but screwing the idle mixture all the way in.

Last time I had this the throttle plates were too far open causing the transition fuel circuit to open.
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Old 07-02-2005, 08:02 AM   #10 (permalink)
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Unresponsive Holley idle mixture screws...

I'd check the throttle blade position first. If the blade is exposing too much of the transition slot, the mixture screw will have no effect just as you describe.
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Old 07-02-2005, 01:33 PM   #11 (permalink)
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Unresponsive Holley idle mixture screws...

The clue is that when the idle screws don't kill the motor, it's getting fuel from somewhere. All the usual suspects have been mentioned - power valve or gasket (lot of problems here as the gaskets don't seem to seal well anymore), metering block gasket seeping or idle transfer slots too far exposed.
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Old 07-02-2005, 03:47 PM   #12 (permalink)
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Unresponsive Holley idle mixture screws...

That 600 RPM idle make one wonder if it's the throttle plates (seems like that would raise the idle), but I know I've gotten into some really crazy tail-chasing before going between idle mixture, idle throttle adjustment front and rear (that's a big culprit), and vac advance, and before too long none of it's working right. Since the carb has been sitting and a little suspect I'd probably go through it and replace all the gaskets and clean it out anyway, then set the throttle blades so that the transfer slots are more or less "square" when viewed from the bottom, give yourself the 1 1/2 turns on the mixture screws, and start from the beginning. Then ship it in to Jesse.

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[ This Message was edited by: 69convert on 7/3/05 3:49am ]
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Old 07-05-2005, 02:55 PM   #13 (permalink)
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Unresponsive Holley idle mixture screws...

i had same problem, and vacum ,should be checked with car in gear,with a vacum gauge ,and if you get say 6 in,put in a lower number say 5 ,always best bet is spend the money on a holley book, by holley,i also had to drill 1/8 holes in throttle plates, to allow the plates enough flow to drop down, as per overlap of cam, but the holes are last ,resort, as the factory holley performace 2 barrel has them from holley, bill
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