Engine backfiring - The 1947 - Present Chevrolet & GMC Truck Message Board Network

1971ChevyTruck · 05-11-2005, 08:22 PM

I just put the engine in my 71 anf it back fires once it is warmed up...any ideas???

68w/sbc406 · 05-11-2005, 09:07 PM

timing

**VetteVet** · 05-12-2005, 12:18 AM

Sounds to me like the carb idle is too lean if it runs ok while the choke is on and then it backfires when it's warmed up. try turning the idle screws out one turn each. The best way is to set them with a vacuum gage.

67chevemall · 05-12-2005, 10:54 AM

Where do you guys hook your vacuum gauges up to????
I would go with the mixture screws aswell. 1 turn

**VetteVet** · 05-12-2005, 04:23 PM

http://www.classictruckshop.com/club...ts/vac/uum.htm You will need to have full manifold vacuum, so connect the gage where it reads manifold vacuum below the carb. Use this link for info.

CHEVIBUBBA · 05-13-2005, 02:36 AM

Quote:

Originally Posted by 1971ChevyTruck

I just put the engine in my 71 anf it back fires once it is warmed up...any ideas???

some more details will help.
is it backfiring all the time?
just when you step on the pedal?

05-11-2005, 08:22 PM	#1
1971ChevyTruck Registered User Join Date: Jan 2005 Location: Illinois Posts: 1,006	Engine backfiring I just put the engine in my 71 anf it back fires once it is warmed up...any ideas???

05-11-2005, 09:07 PM	#2
68w/sbc406 Got Light Emitting Diode? Join Date: Apr 2004 Location: Newberg, OR Posts: 2,485	timing __________________ 1968 1/2 ton 2wd lwb 6 lug disc and bags up front. Next c notch and rear bags '02 Chevy Silverado LT ext cab short bed 2WD 5/7 drop on 22's(the family car) 1993 Cherokee work ride/weekend wheeler

05-12-2005, 12:18 AM	#3
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,709	Sounds to me like the carb idle is too lean if it runs ok while the choke is on and then it backfires when it's warmed up. try turning the idle screws out one turn each. The best way is to set them with a vacuum gage. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

05-12-2005, 04:23 PM	#5
VetteVet Msgt USAF Ret Join Date: Jan 2005 Location: Kalamazoo, Michigan Posts: 8,709	vacuum gage http://www.classictruckshop.com/club...ts/vac/uum.htm You will need to have full manifold vacuum, so connect the gage where it reads manifold vacuum below the carb. Use this link for info. __________________ VetteVet metallic green 67 stepside 74 corvette convertible 1965 Harley sportster 1995 Harley wide glide Growing old is hell, but it beats the alternative.

05-12-2005, 10:54 AM	#4
67chevemall Registered User Join Date: Apr 2003 Location: NB Posts: 3,367	Where do you guys hook your vacuum gauges up to???? I would go with the mixture screws aswell. 1 turn



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