sputtering help!!! - The 1947 - Present Chevrolet & GMC Truck Message Board Network

kpf · 09-21-2002, 09:11 PM

i have a 71 gmc.

I am running a performer manifold on a small block with a carter 600 cfm. I also have a stock hei distributor.

The truck idles fine, runs great with a little throttle bit at medium throttle I will get a backfire. If I give more than medium throttle I do not get a backfire. Then when I come to a stop light (after the truck has backfired) It idles really rough like there is water in the distributor cap or something, but runs fine when I go again. So I stop and turn the truck off for 5 minutes or so and restart and it idles fine but then once it backfires at medium throttle then it idels crappy. I've cleaned the carb really good and downloaded edlebrocks manual and adjusted everything correctly.

I've checked the timing (12 btdc), replaced the cap and rotor recently.

Help!!!!! (going nuts trying to figure this one out)

tom hand · 09-21-2002, 09:33 PM

When you say "backfire" are you talking about it coming from the carb or exhaust?

Kman · 09-21-2002, 10:53 PM

run your plug wires you may have one crossed

1971LT1SWBPOSI373 · 09-21-2002, 11:47 PM

that might be a bit much on the timing (12 degree's), maybe try 8 degree's and see if that helps.

chevy72402 · 09-22-2002, 12:50 AM

I agree with Tom where is it backfiring??? the carb or tailpipe?

kpf · 09-22-2002, 12:03 PM

it backfires out the carb

jhow66 · 09-22-2002, 04:26 PM

Try moving pump lever in one hole. Sounds like a lean backfire. If this does not help,go up on squirter 2 sizes.

Lippyp · 09-23-2002, 04:52 AM

Sticking inlet valve? I had similar symptoms, truck would backfire through carb (Carter) and run rough. Bunged a load of carb cleaner through the carb and fuel system cleaner in the next few tanks of gas and the problem went away. I now just put some fuel system cleaner in about every tenth tank of gas (I don't do a huge number of miles) Gotta be a worth a try as it's not gonna cost you much.

tom hand · 09-23-2002, 08:38 AM

Vacuum leak at base gasket, would be the first thing I would look at. Are you useing the correct adapter to mount the sqaure bore carb on the spead bore manifold?

09-21-2002, 09:11 PM	#1
kpf Registered User Join Date: Jun 2002 Location: Camas, Wa Posts: 58	sputtering help!!! i have a 71 gmc. I am running a performer manifold on a small block with a carter 600 cfm. I also have a stock hei distributor. The truck idles fine, runs great with a little throttle bit at medium throttle I will get a backfire. If I give more than medium throttle I do not get a backfire. Then when I come to a stop light (after the truck has backfired) It idles really rough like there is water in the distributor cap or something, but runs fine when I go again. So I stop and turn the truck off for 5 minutes or so and restart and it idles fine but then once it backfires at medium throttle then it idels crappy. I've cleaned the carb really good and downloaded edlebrocks manual and adjusted everything correctly. I've checked the timing (12 btdc), replaced the cap and rotor recently. Help!!!!! (going nuts trying to figure this one out)

09-21-2002, 09:33 PM	#2
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	When you say "backfire" are you talking about it coming from the carb or exhaust? __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

09-21-2002, 11:47 PM	#4
1971LT1SWBPOSI373 Registered User Join Date: Mar 2002 Location: Springfield, VA Posts: 460	that might be a bit much on the timing (12 degree's), maybe try 8 degree's and see if that helps. __________________ 1971 Shortbed 350/350 w/ Posi-traction 3:73's 1996 Chevy Silverado TJ in Springfield, Virginia Likes old Chevy trucks Drinks Miller MGD

09-22-2002, 12:50 AM	#5
chevy72402 FARMER/RANCHER Join Date: Apr 2001 Location: SD Posts: 597	I agree with Tom where is it backfiring??? the carb or tailpipe? __________________ 1972 chevy super, long box, 402 big block (2,000 miles on rebuild) 2wd tach, tilt, tool box on bedside, a/c, sliding rear window, orange and white. 1972 Chevy Blazer 2wd, tach, tilt, a/c, my first engine overhauling experience, Orange, with white top 2006 Gmc Sierra, XM, Z-71, dark blue, onstar, leather, rear entertainment (audio only) heated seats, (the wife loves that feature) upgraded tires immediately after purchase to Goodyear Wrangler AT/S (hate those rock throwers that come from the factory) BWC

09-22-2002, 04:26 PM	#7
jhow66 Registered User Join Date: Jun 2002 Location: Knoxville Tenn. Posts: 3,058	Try moving pump lever in one hole. Sounds like a lean backfire. If this does not help,go up on squirter 2 sizes. __________________ 56 Chevy Bel-Air 2dr. HT (purchased new) 71 Chevy Cheyenne SWB PU (502HO) 65 GMC short bed step--work in progress and my gofer

09-21-2002, 10:53 PM	#3
Kman Registered User Join Date: Sep 2002 Location: Melbourne,Florida Posts: 174	run your plug wires you may have one crossed

09-22-2002, 12:03 PM	#6
kpf Registered User Join Date: Jun 2002 Location: Camas, Wa Posts: 58	it backfires out the carb

09-23-2002, 04:52 AM	#8
Lippyp English Chevy Owner Join Date: May 2002 Location: Shropshire, UK/ Lot, France Posts: 1,848	Sticking inlet valve? I had similar symptoms, truck would backfire through carb (Carter) and run rough. Bunged a load of carb cleaner through the carb and fuel system cleaner in the next few tanks of gas and the problem went away. I now just put some fuel system cleaner in about every tenth tank of gas (I don't do a huge number of miles) Gotta be a worth a try as it's not gonna cost you much. __________________ Phil '67 C10 long fleet. 350/TH350, 4 bbl Carter, K&N, Dual exhaust, loads of stuff coming soon 2001 S10 Blazer Daily Driver, bone stock 4 door 4x4 with manual transmission

09-23-2002, 08:38 AM	#9
tom hand CCRider Join Date: Feb 2000 Location: Olive Branch,MS,USA Posts: 2,232	Vacuum leak at base gasket, would be the first thing I would look at. Are you useing the correct adapter to mount the sqaure bore carb on the spead bore manifold? __________________ 72 GMC Sierra SWB almost finished---- 84 Softail Olive Branch MS

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