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Old 10-10-2003, 08:31 PM
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Idle Screws Do Nothing?? (holley)

On my 600 cfm Holley carb (4160 converted to a 4150) the idle screws have little to no affect on the idle. The right one has no affect at all, the left one if ran all the way in will make it stutter but that's about all. The cam is a little above stock but nothing radical. Where is the problem??
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Old 10-10-2003, 09:16 PM
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My guess is the fuel is bypassing in the gasket on the front plate. Plate could be warped, or body could be warped too. Plate could be cracked or possible partially plugged.

Having run lots of Holleys and given up on ever having one run right for more than 6 months at a time, i'm now back to Qjets.
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Old 10-10-2003, 09:21 PM
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check the spark timing, check the float levels, and check the fuel pressure.
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Old 10-10-2003, 09:24 PM
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Idle air bleeds could be restricted or plugged.
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Old 10-10-2003, 09:44 PM
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See if hand choking it helps.
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Old 10-10-2003, 10:00 PM
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If the screws aren't doing anything the carb is flooding somehow. Check your float levels again on flat ground.
Immediately after you shut your engine off, look down the carb throat. See if there is any gas coming out of the boosters.
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Old 10-11-2003, 07:04 AM
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You said you converted a 650 to a 600. 650 was a double pumper? You might want to make sure the idle air bleeds are correct for your application, air bleeds that are the wrong size will make your idle mixture screws un-responsive.

A blown power valve dumping allot of fuel through the carb might make the idle screws seem unresponsive too. You probably need to take it apart and look everything over real well.

Oh yeah, last but not least the secondary throttle stop closing point setting can really muck up your idle. If it's closed too far you will have to open up the primaries more at idle which can expose the idle transfer slot and dump allot of fuel at idle which will make the mixture screws seem inoperative.

Hope this helps.
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Old 10-11-2003, 07:20 AM
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Quote:
Originally posted by Goldduster360


Oh yeah, last but not least the secondary throttle stop closing point setting can really muck up your idle. If it's closed too far you will have to open up the primaries more at idle which can expose the idle transfer slot and dump allot of fuel at idle which will make the mixture screws seem inoperative.

Hope this helps.
This is more than likely the problem. The transfer slot should only be exposed no more than .020 at idle in order for the air/idle screws to function properly. If you are having to open the primary throttle plates to keep the engine running you can close it back down and open the secondary plates slightly. The adjustment screw for the secondaries is on the bottom of the base plate on the passenger side. A very small short screwdriver can be used to adjust it without removing the carb. Once the primary plates are closed, you should be able to adjust the air/idle screws. Set them at 1 1/2 turns open as a starting point.
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Old 10-11-2003, 08:22 AM
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Does this carb have idle screws on the secondary side?if so,try turning them all the way in.If the conversion was done incorrectly,the secondary plates could be hanging open a bit too,which would cause the carb to idle off the secondary side.I also second the recommendation that you try to hand choke the car.Sometimes a bit of debris will get stuck in the idle air bleed passages and could cause the car to idle dead rich.You hand choke the carb by racing the engine up from under the hood and then slapping your hand down over the choke horn for about 1 second.As the engine bogs down,pull your hand off and clear the engine out by flashing the throttle once or twice.Prepared for your hand to stink like gas,but this setup will draw out any trash out of the air bleeds on the primary side of the carb.Check all the stuff I mentioned and let us know what you find.BTW,check for vacum leaks too.
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Old 10-11-2003, 09:38 AM
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I opend the secondary plates a little and things improved dramaticaly. I hate to admit it but I didn't know there was an adjustment for the secondary plates. I thought they were to be completely closed at idle. I'm going to open them a little more to see if things get even better.

What would be an indicator that I have opened them too far?
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Old 10-11-2003, 09:42 AM
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Quote:
Originally posted by STBR

What would be an indicator that I have opened them too far?
Not being able to get your idle in gear down to the RPM you want to set it.
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Old 10-11-2003, 09:49 AM
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Even though it's running much better the idle screws still don't seem to do much and it's idling down farther than it should when put in gear so I'm going to open them up a little farther.

Thanks for the help I really appreciate it.
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