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

combustion · 03-22-2007, 04:13 AM

everytime i puch the as on my truck after i let go of the gas it backfires extremely loud (even more when i puch it). its a gen 5 454 with an eddie mani and 750 carb. could this be because im running too rich? or my timing is off?

brak · 03-22-2007, 04:39 AM

probably a combination of the two, but i would start with the timing.

combustion · 03-22-2007, 04:58 AM

Quote:

Originally Posted by brak

probably a combination of the two, but i would start with the timing.

well i cant tune the dam carb thats the thng. its an edelbrock carb. i have to swich out jets and things. but i do not think im overcarbureting it. its not that big of a carb

brak · 03-22-2007, 05:51 AM

Quote:

Originally Posted by combustion

well i cant tune the dam carb thats the thng. its an edelbrock carb. i have to swich out jets and things. but i do not think im overcarbureting it. its not that big of a carb

not sure why you wouldn't be able to tune an edelbrock carb...

in the front at the bottom of the carb are two screws, they adjust the idle mixture. doesn't get any easier than that.
also check the operation of your secondaries. if they are sticking open, that could cause your problem, as the mixture will be too rich for the decelerating engine.

combustion · 03-22-2007, 06:02 AM

Quote:

Originally Posted by brak

not sure why you wouldn't be able to tune an edelbrock carb...

in the front at the bottom of the carb are two screws, they adjust the idle mixture. doesn't get any easier than that.
also check the operation of your secondaries. if they are sticking open, that could cause your problem, as the mixture will be too rich for the decelerating engine.

well i tried tem in 3 sttings. rich normal and lean. it still backfires. meaning its not the idle thats messed up. its something else.

68C15 · 03-22-2007, 07:57 AM

am I reading this right? you snap the throttle, let off then snap again. on the last snap it back fires. I get the impression it is backfiring through the carb, ie. burnt/leaking intake valves. if it is coming out the exhaust I would look at the ignition system. (points, dwell, weak coil etc.)

cooters · 03-22-2007, 08:36 AM

intake gasket leaking or header leak will cause backfire on deceleration but on accel, is it backfiring through intake or exhaust? Valve or cam problems will backfire through card on accel. First check timing.

combustion · 03-22-2007, 12:47 PM

Quote:

Originally Posted by cooters

intake gasket leaking or header leak will cause backfire on deceleration but on accel, is it backfiring through intake or exhaust? Valve or cam problems will backfire through card on accel. First check timing.

sorry for not being clear where is was backfiring from. its doing it through the exhaust. i checked for leaks and i got no leaks, it almost sounds like its burning up gasoline that's is left unburned on the exhaust system

68C15 · 03-22-2007, 10:02 PM

next question. is the unburned gas due to fuel delivery or ignition problems? bump the timing up by 4 degrees and retest. let me know if that changes anything.

combustion · 03-23-2007, 12:01 AM

Quote:

Originally Posted by 68C15

next question. is the unburned gas due to fuel delivery or ignition problems? bump the timing up by 4 degrees and retest. let me know if that changes anything.

ok it did go away quite a bit, but now its hard to start due to precombustion. im afraid im gonna mess up my flexplate or starter. im at 16 degrees now in ignition

bandit1 · 03-23-2007, 12:14 AM

Backfiring out the exhaust is usually and ignition problem, check timing dwell ect.

combustion · 03-24-2007, 02:50 AM

Quote:

Originally Posted by bandit1

Backfiring out the exhaust is usually and ignition problem, check timing dwell ect.

UPDATE. it was an ignition problem. my timing gun was broken andreading ahead in advance. it was like 10 degrees in advance, so when i thought i was setting it to 12 degrees i was actualy putting it to 22 degrees in advance. i tried it with another timing gun. that would explain the hash start with what i thought believed "16 degrees" lol

03-22-2007, 04:39 AM	#2
brak Registered User Join Date: Apr 2006 Location: MinneSNOWta Posts: 1,381	Re: Backfire probably a combination of the two, but i would start with the timing. __________________ 2003 GMC Sierra 1500 WT 1995 Nissan Hardbody 2016 Hyundai Veloster Turbo DC2 (SW/AW) Clyde W. Harvey USN "Socialism is a philosophy of failure, the creed of ignorance, and the gospel of envy, its inherent virtue is the equal sharing of misery" Winston Churchill

03-22-2007, 07:57 AM	#6
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	Re: Backfire am I reading this right? you snap the throttle, let off then snap again. on the last snap it back fires. I get the impression it is backfiring through the carb, ie. burnt/leaking intake valves. if it is coming out the exhaust I would look at the ignition system. (points, dwell, weak coil etc.)

03-22-2007, 08:36 AM	#7
cooters Senior Member Join Date: Oct 2006 Location: Edmonton Alberta Posts: 458	Re: Backfire intake gasket leaking or header leak will cause backfire on deceleration but on accel, is it backfiring through intake or exhaust? Valve or cam problems will backfire through card on accel. First check timing.

03-22-2007, 10:02 PM	#9
68C15 blood type; Retumbo Join Date: Jan 2004 Location: next to my reloading bench Posts: 10,269	Re: Backfire next question. is the unburned gas due to fuel delivery or ignition problems? bump the timing up by 4 degrees and retest. let me know if that changes anything.

03-23-2007, 12:14 AM	#11
bandit1 Registered User Join Date: Jan 2007 Location: Victoria B.C Posts: 35	Re: Backfire Backfiring out the exhaust is usually and ignition problem, check timing dwell ect. __________________ 1969 GMC 910 1970 GMC 1500 custom 1972 yamaha 175 "Money is just like trucks you can never have enough"



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