The thread on backfiring brought this to mind.

When I went through A&P Mechanic school we had it hammered into us that
what was commonly called a "backfire" wasn't really a backfire. The
blast out the exhaust that occurs when the engine isn't running right
was properly called, we were told, an "Afterfire". "Backfires" it was
said, are fuel burning related activities that blow gases back out
through the intake system. Faulty valve timing and ignition timing being
the primary culprits triggering firing backwards  through the intake
system.

The engine mechanic instructors were quite adamant that we get the
differences  stuck in  our heads and use the terminology correctly. Woe
be unto the student that called it incorrectly on a mis-firing engine.
We were taught that the importance of the distinction bore on the the
idea of where to begin a diagnosis as to what problem an engine may
have. Blowing out the intake pipes indicated one direction to go. Going
out the back meant another direction to go in the diagnosis.

Just thought I would pass that bit of detritus along.

Regards,

John Rodgers
88 GL Driver