IML: Misfiring/backfiring...

[commenace@xxxxxxxxxxxx]

Just put about 500 miles on my new 440. ?So it was time for a major tune-up. ?On my way to my friend's work (he's a very gifted Mopar mechanic) the engine starting bogging. ?Misfiring and backfiring out of the tailpipe. ?After the tune-up, new plug wires, plugs, timing set, carb tuning, we noticed it was "missing" as in running roughly as if a plug was not firing. ?All plugs were firing, but we were still "missing." ?My mechanic theorized I might have an intake manifold leak. ?I tested it by spraying starting fluid where the intake manifold meets the heads. ?It seemed I did have a vacuum leak. ?

I replaced the intake manifold gaskets using aviation gasket sealer (good stuff!). ?Started her up yesterday... ? Guess what? ?Still backfiring! ?I don't really feel it misfiring. ?It seems that all the plugs are firing, but it is backfiring. ?It should be noted that on one particular backfire, my muffler exploded. ?This was completely my fault, I won't get into how, just trust me, it was my fault. ?As such, without a muffler, the engine, obviously feels rough. ?Therefore it's hard to judge whether or not it's running smoothly.

My qusetion (at last!) is: what other problems would cause a backfire out the tailpipe (as opposed to in the carb)? ?Could the timing be too advanced/retarded? ?Would that cause a backfire?

Any suggestions would be greatly appreciated...

John.
1965 Le Baron.


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