Pitts Mufflers on Two Stroke Engines 

Some two strokes need more fuel tank pressure than others. When you use a Pitts style muffler the fuel tank pressure drops, and "could" be too low for your particular engine. The way to test this is to tune up your engine just like you always do, then hold your plane striaght up at full throttle. If the pressure is too low the engine will sputter and probably die instantly. You can try to compensate this by re-tuning it on the rich side and do the test again. If you can't get the engine to hold a tune with the nose up, you will likely have to add restrictors to the Pitts stingers. The stingers are the 2 pipes hanging down from the muffler. The combined total area of the two pipes is substancially greater than the stock muffler, thereby lowering the EGT. EGT is Exhaust Gas Temperature, and every engine has an optimum EGT. If the EGT is too low the engine won't develope full power, if it's too high you will see a high head temperature and poor fuel economy. EGT also sets the stage for back-pressure which is what your fuel tank needs.  
 
This can be corrected by blocking off one of the pipes, or putting restrictors in both pipes. This will raise your EGT to the correct level. You don't need much, just enough to provide adequate Exhaust Gas Temperature and fuel tank perssure. This will not hurt the performance of your engine. In fact, if it's done properly you will see a boost in power similar to a turbo muffler just not as pronounced.

 
Here is a PRIME example of what I'm talking about.
 
I reduced the ID of the stingers 10% (still leaving them very large) The fuel tank pressure was raised 50%, the EGT was raised 2%. And the net yeild was +220 RPM over the original pipes. The engine is slightly quieter too!