Carb Problems

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Mar 21, 2006 | 09:00 PM

bertha66

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Lead Driver

Joined: Oct 2004

Posts: 8,062

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From: Central Oregon

Carb Problems

My 66 Custom cab truck had a 352 in it with only 40k on it and it broke the crank. I put a fresh rebuilt 390 in its place and for some reason my carb will not idle the truck in gear without the choke being set slightly. Took another carb off a 428 and now the truck runs perfect. The first carb ran the 352 great but it don't like the 390. dose anyone know what size jets I should run for a 4bbl 600cfm Holley carb? Thank you for your help.

Mar 22, 2006 | 03:54 AM

banjopicker66

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Joined: Apr 2002

Posts: 3,613

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From: Coal country

Bertha66, the FE guys and gals may be better able to answer this; try posting over there.
Good luck!

Mar 23, 2006 | 11:47 AM

Flyn66dtmn

Elder User

Joined: May 2005

Posts: 581

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From: Montana

if you reinstalled the heat exchanger that is in between the carb and intake my guess would be that you probably put the gaskets in the wrong order. it sounds like a vacuum leak. there is a gasket in the set that has a tab on it and this needs to be on the bottom of the heat exchanger as there is a notch in the heat exchanger on one side and not the other. if this tab is not on the right side of the exchanger there will be a massive vacuum leak. spary the back side of the carb and heat exchanger with starting fuild or WD40 while its running , if the motor changes speed then you have a vac. leak . good luck

Mar 23, 2006 | 09:52 PM

customcab66

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Joined: Jan 2006

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There is no heat exchanger on it. There is a spacer between the carb and the intake and it only used for the pcv line. the problem is not a vacuum leak it is the carb, I have a loaner carb for now and it runs perfect. The loaner carb is a 750 dual feed double pumper off a 428 not sure the jet size the carb is my dads and it has been on the car forever.

Mar 23, 2006 | 10:54 PM

Putt

Posting Guru

Joined: Jul 2003

Posts: 2,232

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From: Colville, Washington

The jet sizes don't make any difference at idle. They have nothing to do with the idle circuit. It sounds like the 750 has more A/F mixture going thru it at idle(typical of double pumpers) than the 600. You might try opening the secondaries slightly with the screw under the secondary linkage on the pass side(where the vacuum can link hooks). That will allow more airflow without speeding up the idle speed screw and allow more adjustability with the idle mixture screws.