I cant say enough about Evolution brand engines. I own three of them, a 46NT and two 61NT's. These engines do not require any break-in period and tuning is almost non-existent. The power of these engines is better than O.S. engines and they cost less. Pitts mufflers for O.S. FX engines also fit these engines. I have NEVER had a dead stick using Evolution engines except for running out of fuel. [/b]