Backfire Help - The 1947 - Present Chevrolet & GMC Truck Message Board Network

kpf · 09-11-2002, 05:01 PM

hey all,

when I give the truck a little gas it runs greaat and when I give it 1/2 or 3/4 throttle it responds fine. However when I give about 1/4 or a little more throttle I get a backfire or pop then I let off or give it more gas and it runs fine. I have a small block with a performer manifiold and carter carb. Could it be the float level or ?
Any help would be greatly appreciated.

Also how do I wire in the dome lights??

bigjimzlll · 09-11-2002, 09:07 PM

I now its not carter..but try www.edelbrock.com and you will find the info you need

Andy4639 · 09-11-2002, 09:30 PM

You didn't give the year. In the earlier years they worked through the head light switch, on the later they worked off of the door jam switches. If you have the first ones and want the second just go to a parts store and buy the switches to put inside the door jams and tie them into the light wire, are run new wire for them. Hope this helped as far as the back firing make sure you have the spark plug wires right.

Sheenanny · 09-12-2002, 11:30 AM

Back to your backfire problem, try checking the PCV valve too.

**COBALT** · 09-12-2002, 01:22 PM

Two things:

1. Accelerator pump. Mine was doing this before I rebuilt the carb. Turns out the accel. pump was broke. I had to feather the gas from a dead stop to keep the engine from doing what you described.

Is it an old carb, or a used one you bought from someone? It may need rebuilding, or at least inspect the pump.

2. Timing. Once I got the carb fixed things were great, but I still got a hesitation. Sometimes (rarely) it would pop and spit. Turns out I had to advance the distributor just a bit more to get the hesitation to go away.

71GMC_3/4T · 09-12-2002, 01:35 PM

FYI: Carter *did* build a Quadrajet. It looks just like a Rochester. I have one and it says Carter right on it, no mention of Rochester. Not sure what years normally, but I took this one off a 73-75 range 1/2T pickup.

wcdrake · 09-12-2002, 03:18 PM

If its not any of the things COBALT recommended, I would also suggest checking your electrical components. My 70 did the exact same thing and it ended up being a badly fouled cap and rotor.

71GMC_3/4T · 09-12-2002, 03:59 PM

Check to see how much you have to move the throttle before gas squirts into the carb. It should start to squirt fairly early. If it doesn't, you can bend the linkage to the squirter (there should be a spec in the rebuild sheet) to get it to start sooner. What you're describing sounds like the pump is almost shot. Rebuild teh carb. Quadrajets are actually pretty easy to do.

09-11-2002, 05:01 PM	#1
kpf Registered User Join Date: Jun 2002 Location: Camas, Wa Posts: 58	Backfire Help hey all, when I give the truck a little gas it runs greaat and when I give it 1/2 or 3/4 throttle it responds fine. However when I give about 1/4 or a little more throttle I get a backfire or pop then I let off or give it more gas and it runs fine. I have a small block with a performer manifiold and carter carb. Could it be the float level or ? Any help would be greatly appreciated. Also how do I wire in the dome lights??

09-11-2002, 09:07 PM	#2
bigjimzlll Senior Member Join Date: Dec 2001 Location: Redding,CA...USA Posts: 4,736	I now its not carter..but try www.edelbrock.com and you will find the info you need __________________ It's called "drag racing" if they called it "tic..tic..WHAM!..BANG! F*&K!!!", they'd have to keep the magazines under the counter with the other men's publications click the clicky to join the site.... http://67-72chevytrucks.com/vboard/payments.php 67 lwb..first hotrod in 25 years..540 best ET is 9.45 @ 141.44 Anderson,CA

09-11-2002, 09:30 PM	#3
Andy4639 Old member Join Date: Jan 2002 Location: Liberty, & Garden City S.C. , U.S. Posts: 19,945	Dome lights You didn't give the year. In the earlier years they worked through the head light switch, on the later they worked off of the door jam switches. If you have the first ones and want the second just go to a parts store and buy the switches to put inside the door jams and tie them into the light wire, are run new wire for them. Hope this helped as far as the back firing make sure you have the spark plug wires right. __________________ 1971 LWB Custom, 6.0LS & 4L80E, Speedhut.com GPS speedometer & gauges with A/C. 20" Boss 338's Grey wheels 4 wheel disc brakes. My Driver Seeing the USA in a 71 Upstate SC GM Truck Club 2013,14 and 2016 Hot Rod Pour Tour http://upstategmtrucks.com/ Get out and drive the truck this summer and have some fun! It sucks not being able to hear! LWB trucks rule, if you don't think so measure your SWB! After talking to tech support at Air Lift I have found out that the kit I need is 60811. Per the measurements I gave them. Ride height of truck inside spring and inside diameter of springs.

09-12-2002, 01:22 PM	#5
COBALT Senior Member Join Date: Sep 2001 Location: Seattle, WA, USA Posts: 5,817	Backfire problem... Two things: 1. Accelerator pump. Mine was doing this before I rebuilt the carb. Turns out the accel. pump was broke. I had to feather the gas from a dead stop to keep the engine from doing what you described. Is it an old carb, or a used one you bought from someone? It may need rebuilding, or at least inspect the pump. 2. Timing. Once I got the carb fixed things were great, but I still got a hesitation. Sometimes (rarely) it would pop and spit. Turns out I had to advance the distributor just a bit more to get the hesitation to go away. __________________ '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.

09-12-2002, 01:35 PM	#6
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	FYI: Carter did build a Quadrajet. It looks just like a Rochester. I have one and it says Carter right on it, no mention of Rochester. Not sure what years normally, but I took this one off a 73-75 range 1/2T pickup. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO

09-12-2002, 11:30 AM	#4
Sheenanny Registered User Join Date: May 2002 Location: Lexington, KY Posts: 23	Back to your backfire problem, try checking the PCV valve too.

09-12-2002, 03:18 PM	#7
wcdrake Registered User Join Date: Jul 2002 Posts: 14	If its not any of the things COBALT recommended, I would also suggest checking your electrical components. My 70 did the exact same thing and it ended up being a badly fouled cap and rotor.

09-12-2002, 03:59 PM	#8
71GMC_3/4T Weapons Of Construction Join Date: Apr 2000 Location: Colorado, USA Posts: 1,095	Check to see how much you have to move the throttle before gas squirts into the carb. It should start to squirt fairly early. If it doesn't, you can bend the linkage to the squirter (there should be a spec in the rebuild sheet) to get it to start sooner. What you're describing sounds like the pump is almost shot. Rebuild teh carb. Quadrajets are actually pretty easy to do. __________________ 1971 GMC 2500, 402/TH400 4.10 Daily Driver Lafayette, CO



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