I installed the engine last year and it has less than 20 hours on it. A month ago my son added 2-cycle mixed gas which caused the engine to run rough but once he figured out what happened changed and ran out the bad gas, I have since changed the gas again and pulled/cleaned the fuel filter. Today, the engine started fine, but would not run over 3600 RPM until I ran it constantly for about 30 minutes. Then it seemed fine while running. However, every time I stopped the motor, the same problem would occur (3600 RPM limit) but could achieve full power after a couple of minutes instead of the 30 minutes. I ran the Suzuki diagnostic software which did not detect any failures. Any ideas? This is making me nuts. Thanks.