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1. 03:55 AM - Re: egt temp (Thom Riddle)
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Noel,
When you used the term "backfire" I mistakingly thought you were
referring to the explosion in the exhaust system phenomenon, which is
what many (maybe most) people erroneously call "backfiring" when in
truth that is an "afterfire". Afterfiring being generally caused by
unburned fuel (from overly rich condition) in the exhaust system
hitting a hot spot and exploding. With your further explanation I now
know you were speaking of firing back through the intake system, which
indeed can be caused by lean condition among others. Thanks for the
clarification.
You are also correct when you state that when the fuel level in the
float bowl is low that would cause a lean condition, whether it is
caused by the fuel supply being exhausted or the float level is set too
low.
I'm well acquainted with the rich of peak and lean of peak situations
and in general, especially with engines that are not fuel injected or
in which instrumentation does not include EGT for every cylinder, your
recommendation to run a bit rich of peak EGT is a good one. However, in
a system with manual mixture control, as long as I'm running at normal
cruise power or less, I generally lean very slowly until the slightest
roughness begins to be noticed and then enrichen mixture until smooth
again. As long as the fuel is of the proper octane and everything else
is normal in the engine, this will yield best fuel economy without
risking the engine in any way. Unfortunately, we don't have a manual
mixture control on our 912UL.
Thom in Buffalo
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