Carb. ? - The 1947 - Present Chevrolet & GMC Truck Message Board Network

72'BBGMCSGCC · 05-30-2002, 07:46 AM

I have the origional carb. on my 402BB and in the morning when I start it, it doesn't fast idle(like the choke not working) .I've checked the choke and the butterfly in the carb. is shut when cold and open when hot.Is there any other reason the truck doesn't fast Idle when cold?

*Zkast* · 05-30-2002, 08:11 AM

Check the fast idle adjustement screw located under the choke housing, on the throttle shaft. You will be able to see it by looking from the front of the carb. Turn the screw in until you hit 1600-1800rpm when the engine is COLD.

Mike C · 05-30-2002, 12:12 PM

At this point in time, I would consider the original to be wore out. Mine started acting up last week. I had bought a JET Stage II for the Jimmy and it is so good, I bought another for my 402. SHould be here in a week or so as it was backordered. Story of my life...

**COBALT** · 05-30-2002, 12:30 PM

Did you just rebuild this thing, or has it been running ok before, but not so good now?

Before you start messing with the idle screw can the fast idle even be set correctly? You should be able to pump the accelerator once before firing up the truck when cold, and preset the butterfly. The idle screw should ride the stepped cam to force the linkage. If that's not happening then I'd say yes mess with the screw. If it is happening, then your preset idle needles at the base of the carb aren't set right, or your idle bleeds are clogged...

05-30-2002, 07:46 AM	#1
72'BBGMCSGCC Registered User Join Date: Nov 2001 Location: Fletcher,N.C U.S.A Posts: 162	Carb. ? I have the origional carb. on my 402BB and in the morning when I start it, it doesn't fast idle(like the choke not working) .I've checked the choke and the butterfly in the carb. is shut when cold and open when hot.Is there any other reason the truck doesn't fast Idle when cold?

05-30-2002, 12:12 PM	#3
Mike C Registered User Join Date: Dec 1999 Location: Austin, TX, USA Posts: 7,728	At this point in time, I would consider the original to be wore out. Mine started acting up last week. I had bought a JET Stage II for the Jimmy and it is so good, I bought another for my 402. SHould be here in a week or so as it was backordered. Story of my life... __________________ 44 Willys MB 52 M38A1 64 Corvette Coupe 68 Camaro 'vert LT1 & TH700 69 Z/28 355 12.6's @110 69 Chevy Short Step 4 1/2"/7" drop 72 Jimmy 4WD 4spd 4" & 35's 02 GMC 2500HD 4x4 Duramax

05-30-2002, 12:30 PM	#4
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Did you just rebuild this thing, or has it been running ok before, but not so good now? Before you start messing with the idle screw can the fast idle even be set correctly? You should be able to pump the accelerator once before firing up the truck when cold, and preset the butterfly. The idle screw should ride the stepped cam to force the linkage. If that's not happening then I'd say yes mess with the screw. If it is happening, then your preset idle needles at the base of the carb aren't set right, or your idle bleeds are clogged... __________________ '69 3/4 ton C20 2wd-350ci/TH400 '69 3/4 ton Custom 20 2wd-350ci/4sp Manual '99 2wd 5.7 Chevy Tahoe Seattle, WA.

05-30-2002, 08:11 AM	#2
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	Check the fast idle adjustement screw located under the choke housing, on the throttle shaft. You will be able to see it by looking from the front of the carb. Turn the screw in until you hit 1600-1800rpm when the engine is COLD.



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