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

**68350** · 01-08-2008, 08:03 PM

K, pickup is a 72 chevy with a 70 GMC 402/th400. When I bought the gmc, it has a little holley 4bbl, something like 400cfm, so I decided to change the carburetor to a quadrajet(came off a beautifully running 350 about a year ago) and know it backfires through the carb and the exhaust. I already checked timing, vacuum, distributor, etc. Has HEI if it matters. It ran FINE til this quadrajet was place on top, so I'm thinking that it needs a kit(the carb has had about 2-300,000 ran through it. It's been rebuilt many times, but has always been a good carb. I'm thinking it just sat too long, and now it needs another rebuild. What do you guys(and gals) think? thanks

69long"n"low · 01-08-2008, 08:08 PM

is it running or just backfiring

**68350** · 01-08-2008, 08:13 PM

will start and rev fine, put a load on the carb, and it sputters and backfires(wants to die), let off the throttle and "pump" it, it will stay running.

01-08-2008, 08:03 PM	#1
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Help? K, pickup is a 72 chevy with a 70 GMC 402/th400. When I bought the gmc, it has a little holley 4bbl, something like 400cfm, so I decided to change the carburetor to a quadrajet(came off a beautifully running 350 about a year ago) and know it backfires through the carb and the exhaust. I already checked timing, vacuum, distributor, etc. Has HEI if it matters. It ran FINE til this quadrajet was place on top, so I'm thinking that it needs a kit(the carb has had about 2-300,000 ran through it. It's been rebuilt many times, but has always been a good carb. I'm thinking it just sat too long, and now it needs another rebuild. What do you guys(and gals) think? thanks __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi

01-08-2008, 08:08 PM	#2
69long"n"low Registered User Join Date: Jan 2008 Location: SURREY BC, CANADA Posts: 278	Re: Help? is it running or just backfiring

01-08-2008, 08:13 PM	#3
68350 Senior Member Join Date: Jan 2002 Location: Williston, ND Posts: 2,999	Re: Help? will start and rev fine, put a load on the carb, and it sputters and backfires(wants to die), let off the throttle and "pump" it, it will stay running. __________________ 68 Chevy CST/10, 50th Anniversary, 327/th400, 373 posi, buckets 68 GMC Shortbox Stepside, 402/th400, Tilt, Tach, Bucket Seats, 3.08 Positraction 69 Chevy Camaro SS, 383, 4 speed, positraction 70 Chevy El Camino SS396, Triple Black, 454/th400, Tach 70 Chevy Shortbox Stepside 4x4, 350/th350, Tilt, Tach, Cab Lights, Bumper Guards, Tow Hooks 70 Chevy 3/4 Longbox, 350/auto, 70k, SURVIVOR 71 Chevy Blazer, CST, 350/auto 71 GMC Sierra K2500, 454, 4 speed, 4.10 posi, 37s 71 Custom/30, Open Road, 350/th400, tilt 72 Chevy Shortbox Fleetside, 496 Stroker/th400, Tilt, Tach, Bucket Seats, 3.42 Posi 72 GMC Sierra Grande 2500. 427/th400, tilt, a/c, tool and stowage, buckets/console, 3.54 posi Last edited by 68350; 01-08-2008 at 08:13 PM.



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