"Casey Wilson" N2310D @ gmail.com wrote in message
news:15kre.3603$1q5.2104@trnddc02...
But how about this particular case when only one side is sooty, Pete.

I'm not clear on your question. Do you mean "one side of the aircraft"?
Whether there's a harmful problem or simply a benign aspect of the
particular operation going on, it wouldn't be surprising for only one side
of the engine exhaust to be affected. As a (completely irrelevant )
example, consider the success of GAMI and their "matched injectors". In
most cases, each cylinder is operating under a very specific, and often
quite unique relative to the other cylinders, set of conditions. This is
true even during normal operation of the engine.

In terms of this specific issue, an overly rich mixture may only be causing
enough unburned fuel to result in noticeable soot on one side (even when the
mixture is technically too rich for all cylinders). Or, you could have a
serious problem such as some portion of the priming system leaking into the
engine during regular operation. The former is probably nothing to worry
about; the latter would be cause for grounding the airplane.

Of course, as far as the primer theory goes, it could be as simple as
someone failing to secure the primer knob before starting the engine. I
admit, I don't have personal knowledge of the details of the priming system
on the 150, so I don't know if it primes only one side of the engine. But
I'm pretty sure that configuration exists on other airplanes, so it might on
the 150.

In any case, all of the above assumes black soot, indicating a rich mixture.
If you're burning oil (white/grey soot) to that degree, then there's
probably something serious going on whether or not the effect is symmetric.
You haven't described the soot in greater detail, so we're still doing the
"if it's this, then...if it's that, then" dance.

As far as the maintenance checks go...I assume that the 100-hour and annual
inspections all included a compression check, which *might* provide
information about the condition of the piston rings. But regardless, the
failure to uncover a cause for a problem is not proof that there's no
problem. It certainly seems to me that, as long as the source of the soot
is undetermined, and as long as there is not a similar effect on other
airplanes on the ramp, someone ought to be trying to figure out what's
causing the soot. It may turn out to be completely benign, but you'd want
to know that for sure, rather than just guessing.

Pete