Very confused on backfire issue!
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Very confused on backfire issue!
I can’t find a previous post that helps me with my problem. I have a very confusing issue of my car backfiring through the carb and randomly running an absolute piece of crap! Before you jump immediately to timing, I have gone through that tons of times. So here is a history on what Ihave done, the setup I have, and what has done and is doing. This is a long post so I hope the space isn’t limited.
I started out with a stock 305 from an 89 Iroc that was converted to a carb. It was running ok but I wanted a bit more power and swapped out the heads for a set a buddy had, make unknown but ported/polished to 64cc, headers into a 3” cat and pipe to glass pack muffler, brand new Holley 600 on an Edelbrock Torquer 2 manifold! This never gained me much more power, I couldn’t even get it do more than squeal the tires! Then one day last summer I tried to spin some rubber and the tranny mount let go, motor rotated forward taking out the fan on the linkage, then it started to run like absolute crap! I had to 2 foot it home to keep it from stalling. I thought that the distributor had slapped the firewall and was damaged. I pulled it to inspect it finding nothing. But rebuilt it with an upgrade kit from Summit. It would start but was still not running good, then started popping through the carb. I went back through the timing and redid it incase I screwed it up, but found it was right. Then I decided to pull the cover and check the chain, and decided while I had it apart I would put a gear set in it instead of the chain. And also a bigger cam while I was in there! None of this made any difference good or bad?! I eventually got it running ok, but it would start and run great one day then next day would go back to running like crap! I would mess around with it for ages, get it running good again only to have it once again go back to running like crap again. This has been my nightmare for months! Won’t start with out a fight, then won’t idle, and occasionally backfire?! I finally got it to co-operate for awhile but not good enough to drive. Then last weekend I had my daughter help me dial it in, and we got it running perfect! This was in the morning, I had restarted it randomly afterwards and it continued running perfect. Then I tried starting it that afternoon after had been sitting about 4 hours, and it went back to running like crap crap again! Fight to start, wouldn’t idle, backfiring through the carb! Nothing had been touched?! Then this morning I went to work on it again for the millionth time, and without touching anything yet, it started easy, ran great, idled good, but when I snapped the throttle it was still backfiring fire ***** through the carb. Only after it had been running for a while and the temp got up in 160degree area the backfiring almost went away, instead of backfiring every snap it would just do it occasionally? Although if I just ran the throttle in a normal manner it doesn’t backfire at all?! The random way it’s acting is what confuses me? I have never had a car do this before!
So here is what I have done most recently: pulled heads and had them and the intake surfaces checked and they were good, engine block was flat and in great condition, and head gaskets were looking properly sealed, the original valves to those heads looked good so were reused with new seals, distributor is brand new and rebuilt with an upgrade kit from Summit the middle springs in the kit were used and adjustable vacuum pod installed, new plugs and wires, Lunati Voodoo cam and flat tappet lifter kit from Summit broke in to the letter by the instructions supplied, gear drive timing set from Summit, brand new Holley 600.
It is set at 12degrees BTC initial, 34degrees total advance by 3500rpm and holds there through 4200, curb idles at 750rpm anything lower and it stumbles a lot, idles around 500-600rpm in gear. Starts at first touch of the key, runs good and seems to rev up good at normal throttle pressure. Just backfiring now under snapping of the throttle until temp is around 160.
I don’t know what more I can do, and I don’t trust it to leave the drive way! Hopefully someone can shed some light on this for me. I was wondering about the springs in the dist, and/or the adjustable vacuum pod, or possibly burnt valves? Any help is greatly appreciated!
I started out with a stock 305 from an 89 Iroc that was converted to a carb. It was running ok but I wanted a bit more power and swapped out the heads for a set a buddy had, make unknown but ported/polished to 64cc, headers into a 3” cat and pipe to glass pack muffler, brand new Holley 600 on an Edelbrock Torquer 2 manifold! This never gained me much more power, I couldn’t even get it do more than squeal the tires! Then one day last summer I tried to spin some rubber and the tranny mount let go, motor rotated forward taking out the fan on the linkage, then it started to run like absolute crap! I had to 2 foot it home to keep it from stalling. I thought that the distributor had slapped the firewall and was damaged. I pulled it to inspect it finding nothing. But rebuilt it with an upgrade kit from Summit. It would start but was still not running good, then started popping through the carb. I went back through the timing and redid it incase I screwed it up, but found it was right. Then I decided to pull the cover and check the chain, and decided while I had it apart I would put a gear set in it instead of the chain. And also a bigger cam while I was in there! None of this made any difference good or bad?! I eventually got it running ok, but it would start and run great one day then next day would go back to running like crap! I would mess around with it for ages, get it running good again only to have it once again go back to running like crap again. This has been my nightmare for months! Won’t start with out a fight, then won’t idle, and occasionally backfire?! I finally got it to co-operate for awhile but not good enough to drive. Then last weekend I had my daughter help me dial it in, and we got it running perfect! This was in the morning, I had restarted it randomly afterwards and it continued running perfect. Then I tried starting it that afternoon after had been sitting about 4 hours, and it went back to running like crap crap again! Fight to start, wouldn’t idle, backfiring through the carb! Nothing had been touched?! Then this morning I went to work on it again for the millionth time, and without touching anything yet, it started easy, ran great, idled good, but when I snapped the throttle it was still backfiring fire ***** through the carb. Only after it had been running for a while and the temp got up in 160degree area the backfiring almost went away, instead of backfiring every snap it would just do it occasionally? Although if I just ran the throttle in a normal manner it doesn’t backfire at all?! The random way it’s acting is what confuses me? I have never had a car do this before!
So here is what I have done most recently: pulled heads and had them and the intake surfaces checked and they were good, engine block was flat and in great condition, and head gaskets were looking properly sealed, the original valves to those heads looked good so were reused with new seals, distributor is brand new and rebuilt with an upgrade kit from Summit the middle springs in the kit were used and adjustable vacuum pod installed, new plugs and wires, Lunati Voodoo cam and flat tappet lifter kit from Summit broke in to the letter by the instructions supplied, gear drive timing set from Summit, brand new Holley 600.
It is set at 12degrees BTC initial, 34degrees total advance by 3500rpm and holds there through 4200, curb idles at 750rpm anything lower and it stumbles a lot, idles around 500-600rpm in gear. Starts at first touch of the key, runs good and seems to rev up good at normal throttle pressure. Just backfiring now under snapping of the throttle until temp is around 160.
I don’t know what more I can do, and I don’t trust it to leave the drive way! Hopefully someone can shed some light on this for me. I was wondering about the springs in the dist, and/or the adjustable vacuum pod, or possibly burnt valves? Any help is greatly appreciated!
Joined: Nov 2008
Posts: 2,093
Likes: 175
From: Milwaukee
Car: 92 Firebird, 77 Trans Am SE, 86 Z28
Engine: 5.7 HSR, T/A 6.6, empty
Transmission: T-5, TH350, T-5
Axle/Gears: 3.08 posi, 3.23 posi, 3.23
Re: Very confused on backfire issue!
I'd be looking into that carb. The occasions I've had a backfire through a carb was from it being lean. The infrequency of the issue would have me question the carb or the distributor weights hanging up instead of moving freely. Not being a fan of edelbrock carbs would send me there first, and that's out of bias so I could accuse it just for spite.
If it were a backfire from the exhaust, then I'd be more worried about poor spark of some kind.
Hope you find whatever it is, report back to us when you find it.
If it were a backfire from the exhaust, then I'd be more worried about poor spark of some kind.
Hope you find whatever it is, report back to us when you find it.
Senior Member
Joined: Mar 2017
Posts: 902
Likes: 139
From: waterloo ontario
Car: 1986 trans am
Engine: 305/350
Transmission: 5 speed
Axle/Gears: 3.27
Re: Very confused on backfire issue!
the gear drive is notoriously finicky and not for a mild street car at all,the sound is reminiscent of a power steering pump badly needing fluid(im looking at you ford)
you actually did your car a dis-service putting it in instead of a good double row timing chain,you introduced more potential problems with no benefit.
it almost seems like you hurt the motor when you ripped the trans mount out over revving it possibly?
it seems like a lean condition,timing gears out of synch or intermittent spark to me.hope you figure it out
you actually did your car a dis-service putting it in instead of a good double row timing chain,you introduced more potential problems with no benefit.
it almost seems like you hurt the motor when you ripped the trans mount out over revving it possibly?
it seems like a lean condition,timing gears out of synch or intermittent spark to me.hope you figure it out
Thread Starter
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Joined: Aug 2012
Posts: 3
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Re: Very confused on backfire issue!
Thanks for the help guys, I was actually at the shop working on it today when I got your reply aliceempire, so that was good timing! Lol. I tried your suggestion about the carb and adjusted the mixture a bit richer. I originally had it adjusted 1.5turns out. I made adjustments a 1/4turn at a time, and at 2.5turns it finally started to act happier and the backfiring seems to have quit. I won’t say it’s fixed yet cuz this nightmare has done this before, run great today and crap tomorrow. I will update in a few days if it continues to work right.
1986 BANDIT, I don’t know what problems may come about from the gear drive, and hopefully I won’t have any, but I have wished I didn’t put them in due to the noise. I knew they were noisy but these are ridiculous, and yes it sounds like an old Ford power steering pump, mainly a 1980’s truck! Lol
1986 BANDIT, I don’t know what problems may come about from the gear drive, and hopefully I won’t have any, but I have wished I didn’t put them in due to the noise. I knew they were noisy but these are ridiculous, and yes it sounds like an old Ford power steering pump, mainly a 1980’s truck! Lol
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