RE: IML: Misfiring/backfiring...

["Robin Giesbrecht" <robings@xxxxxxxxxxx>]

How much vacuum are you pulling at idle? Putting a vacuum gauge on it will 
tell you a few things that you need to know. A good stock big block should 
pull close to 20" at idle with no fluctuation.You can get the timing pretty 
close by moving the distributor for maximum vacuum at idle.I am just 
wondering why you used sealer on the intake gaskets? Were they new gaskets? 
What kind of sealant? I have been an aircraft mechanic for 20 years and some 
material the aviation world uses is real good and some is not so good. A lot 
of it is for very specific purposes. Here is a stupid qhestion. Are you sure 
that the plug wires are all connected to the right plugs(firing order)? A 
big V8 will run with a couple of cylinders out of sequence but it won't run 
real well.

Robin Giesbrecht
1972 Imperial

> From: commenace@xxxxxxxxxxxx
> Reply-To: mailing-list@xxxxxxxxxxxxxxxx
> To: mailing-list@xxxxxxxxxxxxxxxx
> Subject: IML: Misfiring/backfiring...
> Date: Mon, 08 Aug 2005 12:33:56 -0400
>
> 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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