"Tim Mara" wrote in message
...
we had a similar problem years ago with a Pawnee 150.....would usually run
up fine on the ground but every couple of flights just after take-off when
you were expecting it to get up to full RPM it would only get about 80% of
the normal power ....unfortunately this was about the time you'd be
lifting off with a glider on behind.....the mechanic replaced carburetor
float, changed plugs, adjusted magneto's .all resulted in the same
behavior...then finally we checked the exhaust and sure enough a baffle
had broken off inside and sometimes would lay harmlessly away from the
muffler inlet or exit and other times would just simply end up plugging
the exhaust end of the muffler.....what goes in has to come out or less
can come in and consequently when less comes in and out the motor doesn't
work as intended...you might also notice a higher than normal engine
temperature as an indication that this is the problem ...anyway, this is
my bet!
tim

Please visit the Wings & Wheels website at www.wingsandwheels.com

We did find problems with the baffling inside the muffler over the winter
and thought it was our "aha" moment. The muffler was rebuilt but the
problem remains.

Bruce