On 7 Aug 2003 at 14:08, Douglas Frank wrote:
> What causes it? There are two kinds I guess: either in the intake, or
> the exhaust.
Hi, Doug. You'll probably gets lots of good replies. Whether it is
intake or exhaust depends on whether you mean backfiring or
frontfiring. :-)
Actually, backfiring per se is gas burning in the exhaust system.
This happens when enough unburned gas escapes into the exhaust from
one or more cylinders, and then something ignites it. The ignition
could be from burning gas being released by one or more cylinders or
a serious hot spot in the exhaust system or the manifold or on a
valve. (I once saw a truck straining through the Callahan Tunnel
with a catalyst glowing *BRIGHT RED*, and every few seconds it let
out a devilishly loud BANG! It was not a comforting situation.) In
a street engine the presence of so much unburned gas in the exhaust
is a sign that one or more of the cylinders isn't firing well.
I've seen similar spitting up through the carb. This means that
flame is somehow squeezing out through the intake valve. Possible
causes might be a burned valve or one adjusted way too tight, or
timing that is so far off as to ignite the cylinder's contents before
the valve closes sufficiently.
--
Jim Muller
jimmuller@pop.rcn.com
'80 Spitfire, '70 GT6+
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