"john smith" wrote in message
...
We just did the annual on our 1945 Aeronca Champ.
Took the plugs out to do the compression test.
On inspecting them, noted that they were black, sootie.
The AI said that is normal for autogas in a Champ.

Honeck always says his plugs are clean when he runs autogas.
Is this the difference beween having a low compression, low horsepower,
no-mixture control engine and having a high compression, high
horsepower, mixture controlled engine?

Some of those old Continental A-65 engines have mixture control, most don't.
I fly one that does but the plugs still get dirty. I use a little 100LL
occasionally to help the valves and seats. Try an additive to keep them
from fouling and clear your engine by gently revving it up for a couple of
seconds on the ground and on final. (BTW, I just read in the O-300
Continental manual where it says to "gun" your engine on final to clear it.)
A Marvel-Schebler carburetor has a better mixture control than a Stromberg,
the carb hanging from most A-65's. And most of the Strombergs have been
safety-wired to full rich.