Exhaust problems with the Top 80
Tip from Bill Stoll
Rarely, the exhaust system can get clogged with soot. When this happens, top end performance of the engine will decline because of the greatly increased pressure in the system.
The output area of the exhaust system has a long aluminum pipe inside the muffler filled with small holes. The exhaust gases go through these small holes and then exit the end of the pipe. The holes are about 5mm (3/16") in diameter. If the engine is running very rich (carburetor misadjusted/defective), unburned fuel (soot) can slowly build up around these holes and restrict the movement of exhaust gases through the system.
To remove these deposits, use a 20mm wide brass tube cleaning wire brush (like this one). Move the brush back and forth until all soot deposits are removed. This may take some time and effort to remove the deposits completely. Check with a flashlight.