Unburnt fuel/exploded muffler
Thread Starter
Intermediate
Joined: Mar 2011
Posts: 27
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Unburnt fuel/exploded muffler
I have a 72 vette, roch.quadrajet. Car has been stumbling bad. Carb rebuilt last year. Unable to fix stumbling. New exhaust put on this year. We thought stumbling caused by carb problem after trying point And timing adjustment. Removed carb and sent to rebuilder who replaced accelerator pump. C
When setting up car after reinstall, still stumbling, then really loud backfire. Car smoothed out, ran well for about 3 hours, then stumbling Again. Tonite, revving car and another loud backfire-my muffler exploded. But car still missing and stuttering. Any help appreciated.
When setting up car after reinstall, still stumbling, then really loud backfire. Car smoothed out, ran well for about 3 hours, then stumbling Again. Tonite, revving car and another loud backfire-my muffler exploded. But car still missing and stuttering. Any help appreciated.
Le Mans Master
Joined: Jul 2000
Posts: 6,001
Likes: 112
From: Saginaw Michigan
You by any chance have an updated High Energy Ignition (HEI) system (1975 or newer) in your 1972? There is a module inside the distributor that sometimes gets intermittant with age. I blew the mufflers on my 1975 roadster years ago when it cut out and came back suddenly. It didn't help when I pumped the accelerator as the engine died.
I would expect that you could have an intermittant problem with the older points type distributor and coil system as well.
Jim
I would expect that you could have an intermittant problem with the older points type distributor and coil system as well.
Jim
Thread Starter
Intermediate
Joined: Mar 2011
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Thanks. I still have the oringinal distributor and coil on the car. I've been told that i'm dumping too much gas thru, it is collecting in the muffler, and boom. a lean condition would seem to be the opposite. do you have a cite for lars' article?
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
the post was within the past week or so. do a search using his name. he explained that in a rich condition all the oxygen is consumed (assuming that the distributor is set up properly, which by the way, he blames most carb problems upon) by the excess fuel, and therfore it would be impossible for an afterfire to occur. in a lean condition there is excess oxygen in the exhaust that could cause an afterfire.
Racer
Joined: May 2008
Posts: 261
Likes: 7
Did this with an Optispark once--major misfiring issue, dumped loads of unburned fuel into the hot exhaust, it vaporized, and when the car fired again, exploded the muffler. I agree you most likely have a distributor issue.
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Melting Slicks
Joined: Mar 2007
Posts: 2,520
Likes: 11
From: Hinckley OH
Are you running ported or manifold vacuum? I had an afterfire when I had my vacuum advance on manifold vacuum. It went away when I switched to ported vacuum. Maybe I just masked another problem but my engine didn't like manifold vacuum at all.
Thread Starter
Intermediate
Joined: Mar 2011
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still have original ignition system. i'm running ported vaccum. both vaccum and mechanical advance working.
what would be the ignition/distributor problem that could be causing this? timing has been set and checked several times. and why would the first backfire a week or so ago allow it to run well for several hours? i'm stumped. thanks for the help.
what would be the ignition/distributor problem that could be causing this? timing has been set and checked several times. and why would the first backfire a week or so ago allow it to run well for several hours? i'm stumped. thanks for the help.
Le Mans Master
Joined: Jul 2006
Posts: 8,117
Likes: 104
From: charlotte north carolina
lars might post here, but i'll echo what he's said many times-use manifold vacuum for the advance.
also, not to get picky, backfire is though the carb, afterfire is through the exhaust. both are caused by totally different problems.
also, not to get picky, backfire is though the carb, afterfire is through the exhaust. both are caused by totally different problems.
Thread Starter
Intermediate
Joined: Mar 2011
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i can switch it and see what happens.. i suppose that technically mine was an afterfire since it blew the muffler wide open. could a lack of spark in a cylinder allow that much gas to pass thru to the exhaust?
Thread Starter
Intermediate
Joined: Mar 2011
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Thanks. Seems my centrifugal advance was sticking. a little oil on the pad seems to have helped for several days, but now the car is beginning to miss a bit again. Maybe i'll just add a bit more oil and see what happens.