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Old 06-30-2006, 12:13 PM
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Tuning questions.

The vehicle in question is a friends 81 chevy truck with a stock 350. the problem is that when he drives it stumbles and backfires through the carb. so I brought it over to my shop to look at it. when I started it to pull it into the shop it wouldn't idle. it kept reving higher and higher until I shut it down. I thought the linkage was stuck so I opened the hood and check but it was all clear. so then I went to start it again and it had a huge backfire thru the exhaust. it sounded like a gun shot this was followed by emense amounts of black smoke. SO my geuss is the problem lies with the timing but I don't know what to check and was wanting your guys opinions on what to check first.

okay I have an update. I went out and started it back up. It fired right off and was running pretty good. but it was really loud so I checked and I blew the side of the muffler out and that was what the loud noise was. SO I know a clogged cat. can cause drivability issues. But could a clogged muffler cause all the problems that were happening before. If not why did the muffler blow out?

Last edited by comet boy; 06-30-2006 at 01:05 PM.
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Old 06-30-2006, 02:35 PM
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I had the same thing happen years ago in a 79 Malibu I had, this is usually caused by flooding on start up due to the primaries leaking down on a Q-jet carb, or just flooding period. The raw gas and fumes get trapped in the muffler and can`t get out, a good backfire ignites it and boom! Ever burn a high mileage muffler in a fire? 9 times out of ten, it`ll go off like a shotgun several times before it burns out the fuel vapour.
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Old 06-30-2006, 02:51 PM
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combustion in the exhaust


i think lean mixtures can cause this too, ,especailly with retarded timming.

Last edited by spinn; 07-01-2006 at 04:04 PM.
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Old 06-30-2006, 05:08 PM
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yea I figured out why I blew out the muffler but I was wondering what could be causing the drivability issues. it has a demon carb. Which vaccum port is the vaccum advance supposed to be hooked to?? the ported or continuous?? or could the problems be caused by something completey different
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