My BME 102 has lost 350rpm and doesn't seem to have the power it had 80 flight ago. I removed the spark plug and the piston is a tan color. I didn't check the plug gap so I don't know if it is correct. THE muffler is coated in soot like in a wood stove.

Any comments are welcomed!

Check for a stuck ring. The soot indicates that a lot of oil is going through the pipe, meaning it either has to much oil in the mix, or it's going by the ring due to a poor seal.

Good luck!

I don't think it is too much oil.
On my last 6 gallon mix, I added a fuel stabilizer.
Could this be part of the problem?

Geistware, just curious, as much as you fly, why would you add a fuel stabilizer? When I was building custom cars, with aspirated or injected engines, I cautioned my customers from using ANY type of fuel additives. Cleaners, and ESPECIALLY a stabilizer.
A fuel stabilizer "isolates oxygen" and prevents it from escaping the fuel, therefore, neutralizing the corrosives in the fuel. Now think about that, anything that surrounds and encapsulates the oxygen in the fuel is going to inhibit the flash point of the fuel, and anything that neutralizes corrosives, is going to neutralize something else, (like lubricants). I have found that a fuel stabilizer can and will coat the surface of the piston, and sleeve, and can cause valves ( in four strokes), and rings to stick, and in some cases even beak.
Remove the spark plugs, try squirting some carburator cleaner in the exhaust ports and the plug holes, with the spark plugs out and the engine inverted turn it over a lot while constantly spraying cleaner in the exhaust ports. After the fluid turns clear, squirt your favorite oil, unmixed, in the sparkplug hold and rotate to coat all surfaces. Replace plugs and fire her up. see if that helps.

Just an idea. My .02 only.

Wayne

have you pulled the jug and checked for a stuck ring?

Pulling the head (jug) is beyond my ability. I would not know what to do with the jug after I had it in my hot little hands.

What I have done is taken Wayne's advice and filled the engine up with carb cleaner and turned it over until clear. I actually used some morot flush and ran 4 cans through the engine before it was clean. I then took Marvel M Oil and coated the inside of the engine and then turned it over and sat the engine out in the sun.

I put 8 flights on my plane today and it seems to run strong and rich. I will run a couple of gallons through it and see what happens next.

Wayne, also to answer your question about stabilizer, I was told that gas could go bad sitting around for a month. I was suppose to go out of town a couple of weeks ago and figured I would be safe that sorry. I have gone though 20 gallons in 6 weeks so I will agree, I don't need to add stabilizer to my fuel!