My recently-acquired '77 Midget has a backfiring problem when the
accelerator is released suddenly and the engine is winding down (is
"overrunning" the correct term?) Not being much of a engine mechanic, I'm
not real sure where to start, and the material I can find suggests about
25 things to check. Guess what I'm looking for is, if not a short cut, at
least some prioritization.
The engine has a Weber downdraft carb and Mallory dual-point ignition. The
air pump is still installed and functional. It starts readily and runs
nicely, other than the backfiring.
I assume backfiring is caused by an accumulation of unburned fuel mixture
in the exhaust manifold which suddenly ignites? Wouldn't that suggest that
the engine is getting more fuel than can be burned normally, and wouldn't
that suggest too rich a fuel mixture? The only adjustment I can find on the
Weber carb is what I assume to be the idle mixture screw at the bottom of
the carb. How does one adjust the mixture?
There's no smog check requirement here in SC and no vehicle inspection.
Should I remove the air pump? Might it, by supplying nice fresh O2 to the
exhaust manifold, be contributing to the backfiring?
Sorry for the "rank newbie" questions.
Tom
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