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

iufan71 · 03-10-2004, 11:58 PM

I have one other problem with my truck also. When i mash the gas pedal to the floor,the truck seems to bog down. I was told while back,its probably a bad accel. pump on the carb? I live in Indianapolis,anyone around my area that could help me fix this? Or to maybe up their own diagnosis?Thanks.

NeCrOmAnCeR · 03-11-2004, 12:05 AM

I'm down towards Louisville. Will be up there in a few months for a concert if you can wait that long.:p

Before we can guess, we need to know what type of carb. If a stock Q-jet, you're secondary air valve spring could be to loose allowing the secondaries to open to soon. If the truck runs OK with quick throttle openings as long as you don't get into the secondaries I'd bet the accelerator pump is ok. Give us some more details

iufan71 · 03-11-2004, 12:09 AM

I beleive its the factory quadrajet,on the 350. I have tried carb cleaner on it as well,i cant even get the back flapper to open at all when mashing on the gas. Not sure this is related to my problem or not.

NeCrOmAnCeR · 03-11-2004, 12:14 AM

The rear "flappers" as you call them are the secondary air valves. With the truck off you should be able to feel how far the throttle has to be opened to get the secondary throttle blades to open (about 70%) the secondary air valves don't open till after this point. But they only open when the engine has generated a high level of vacuume. You could lock out the secondaries to prevent them from opening at all (it does this automatically when the choke is still applied) and you will be able to find out if the problem is with the secondaries or not. When driving and you floor it, after the bog do you hear the secondaries open???

iufan71 · 03-11-2004, 12:19 AM

No,i dont hear anything,just seems like Im flooding the motor,when i stomp on the gas.

NeCrOmAnCeR · 03-11-2004, 12:25 AM

Does it ever straighten out? Or will it eventually die?
Check the linkage to be sure all the throttle plates are opening, and then try to readjust the secondary air valve.

iufan71 · 03-11-2004, 12:29 AM

I just ease off the gas,and it runs fine,just has no get up and go,like my old 76 with the same setup did.

03-10-2004, 11:58 PM	#1
iufan71 Registered User Join Date: Apr 2003 Location: Indianapolis,IN Posts: 138	Carb Problem? I have one other problem with my truck also. When i mash the gas pedal to the floor,the truck seems to bog down. I was told while back,its probably a bad accel. pump on the carb? I live in Indianapolis,anyone around my area that could help me fix this? Or to maybe up their own diagnosis?Thanks.

03-11-2004, 12:05 AM	#2
NeCrOmAnCeR Registered User Join Date: Feb 2004 Location: Hodgenville, Ky Posts: 735	I'm down towards Louisville. Will be up there in a few months for a concert if you can wait that long.:p Before we can guess, we need to know what type of carb. If a stock Q-jet, you're secondary air valve spring could be to loose allowing the secondaries to open to soon. If the truck runs OK with quick throttle openings as long as you don't get into the secondaries I'd bet the accelerator pump is ok. Give us some more details Last edited by NeCrOmAnCeR; 03-11-2004 at 12:09 AM.

03-11-2004, 12:09 AM	#3
iufan71 Registered User Join Date: Apr 2003 Location: Indianapolis,IN Posts: 138	carb prob I beleive its the factory quadrajet,on the 350. I have tried carb cleaner on it as well,i cant even get the back flapper to open at all when mashing on the gas. Not sure this is related to my problem or not.

03-11-2004, 12:19 AM	#5
iufan71 Registered User Join Date: Apr 2003 Location: Indianapolis,IN Posts: 138	Carb No,i dont hear anything,just seems like Im flooding the motor,when i stomp on the gas.

03-11-2004, 12:29 AM	#7
iufan71 Registered User Join Date: Apr 2003 Location: Indianapolis,IN Posts: 138	Carb I just ease off the gas,and it runs fine,just has no get up and go,like my old 76 with the same setup did.

03-11-2004, 12:14 AM	#4
NeCrOmAnCeR Registered User Join Date: Feb 2004 Location: Hodgenville, Ky Posts: 735	The rear "flappers" as you call them are the secondary air valves. With the truck off you should be able to feel how far the throttle has to be opened to get the secondary throttle blades to open (about 70%) the secondary air valves don't open till after this point. But they only open when the engine has generated a high level of vacuume. You could lock out the secondaries to prevent them from opening at all (it does this automatically when the choke is still applied) and you will be able to find out if the problem is with the secondaries or not. When driving and you floor it, after the bog do you hear the secondaries open???

03-11-2004, 12:25 AM	#6
NeCrOmAnCeR Registered User Join Date: Feb 2004 Location: Hodgenville, Ky Posts: 735	Does it ever straighten out? Or will it eventually die? Check the linkage to be sure all the throttle plates are opening, and then try to readjust the secondary air valve.



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