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Carburetors Carb discussion and questions. Upgrading your Third Gen's carburetor, swapping TBI to carburetor, or TPI to carburetor? Need LG4 or H.O. info? Post it here.

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Old 07-29-2002, 06:33 PM   #1
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Engine: 350 cid.
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High-idle Holley

I rebuilt an old Holley 4175 and have it installed on my car.It fired right up but i can't get it to idle below 1500rpm's.I took the front of it apart again just to see if i screwed something up,but it looks fine.The idle screw is backed out so far that there is hardly any transfer slot showing at all.The idle mixture screws don't do a thing.Anybody got any ideas?I know this carb doesn't have the best reputation in the world,but the thing should idle lower than this.Just so you know,there are no vacuum leaks that i can detect,(Q-jet i had on it idled fine)and i've got the vacuum advance hooked to ported,(tried both ways)Choke linkage works fine(goes open quickly,fast idle disengages)I'm real close to putting my q-jet back on,but i wanted to give this old girl an honest effort.(I know,i know,you told me so Five7kid)
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Old 07-29-2002, 06:38 PM   #2
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If the blades are closed and it still idles..especially high...air MUST be getting in somewhere else. IE a vacuum leak.
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Old 07-29-2002, 08:46 PM   #3
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Thats the first thing i thought of too,but for the life of me,i can't see where it would be leaking.i used new gaskets and the carb is in real good shape.I 'm pretty sure i plugged any vacuum ports that aren't being used,but i'll check everything again.I even checked the throttleshaft for excessive play.Is there a spot somewhere on Holley's that is prone to vacuum leaks?
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Old 07-30-2002, 10:12 AM   #4
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This is a long shot cause I don't have a 4175 to eye ball
but do you have a carb air filter stud in the top of the carb?
If not, does this threaded hole where the carb stud screws into
go all the way down through the carb? Just hold your thumb over the hole to see if this is the air leak.
Are the secondary throttle blades being held open more than they should at idle? Remove the carb and look for a missing screw in the bottom of the baseplate.

Last edited by F-BIRD'88; 07-30-2002 at 10:15 AM.
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Old 07-30-2002, 10:21 AM   #5
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That's one i hadn't thought of,but the aircleaner stud is in the hole,so i guess it isn't leaking there.I'm going to go at this right after work,hopefully i'll be able to find the problem.Thanks for the replies guys.
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Old 08-01-2002, 04:52 AM   #6
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Me too

MTCAMARO,
I'm having the exact same problem. Can't get the idle down on my 4150.
Jester gave me some good ideas but still nothing worked. I'm planning on tearing the carb down again this weekend and re-re-re-rebuilding it "again" to see if i've missed somthing, but just like you, no vacume leaks I can find with water or propane and still I can't get an acceptable idle.
If you figure it out first, please let me know...I'm stumped as well
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Old 08-02-2002, 11:58 AM   #7
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I'd take a look at those secondary blades. They may be being held open too much, either by the set screw or by the linkage.

RB83L69 seems to think those 4175's are the cat's meow. You might shoot him a PM and see if he can help.
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Old 08-02-2002, 04:05 PM   #8
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Check the secondary blades AND the throttle cable. If you arent using the correct bracket sometimes the cable wont allow the throttle to close all of the way. An easy way to test this is to disconnect the cable and start the car.
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Old 08-03-2002, 07:40 PM   #9
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I had to break down and put my Q-jet back on for now,the car has been down for three days and i'm fresh out of ideas.The throttle cable was actually unhooked for most of the trouble shooting and the secondary blades looked like they were shut all the way,but i'll make sure now that i can hold it in my hand.I'll check that set screw also Five7.I shot Holley's Tech help line an e-mail,but i haven't heard back yet.I'll let you (IMARK) know if i learn anything more.
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Old 08-03-2002, 07:56 PM   #10
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It's fixed,

OK MTCAMARO, Now here's where I really sound stupid. When I rebuilt the carb the first time (A) I used the wrong gasket between the body and throttle blades and (B) I used the "safety needles and floats". This time I replaced them all with original Holley Parts. Works great.
Also I double checked the Coil with a spare replaced the Ignition Control Module.
Idle is dead on. Hope this helps
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Old 08-04-2002, 10:19 AM   #11
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Glad to hear things worked out for you IMARK!I got my problem fixed as well,put the thing back on and idles perfectly.I bet i feel about as dumb as you because it turns out that the problem was the secondary throttle blades being open too far.I don't know how many times i looked down there with the carb on the car and they looked closed.Once i took the carb off and looked down the holes,i could see all kinds of daylight .I got almost 2 full turns out of the set screw before they were seated.In my own defence,i didn't touch that screw when i rebuilt the carb,so that might have been the reason someone took it off and sold it on ebay.They couldn't get it to idle either.Anyway,I want to thank everyone who took the time to lend their advice,you guys' have baled me out more than once.
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Old 08-04-2002, 06:27 PM   #12
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Ditto!
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Old 08-04-2002, 06:27 PM
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