Im not too happy with my STS engine right now. When I had it running before the idle was very inconsistent. At idle it would rev really high like it has at quarter throttle. I knew something wasnt right cause my throttle linkage and idle settings were all correct. It sounded like an air leak. BTW this engine is the 21E with a roto start backplate. Also when I got the engine I never took it apart, i just put a glow plug in and broke it in by the book. Its had less than a 1/2 gallon through it and Ive been really impressed the motor so far. So I took out the engine and found that the backplate was loose, so this explains the air leak. Then I took off the backplate and saw that there was thick grime inside the engine and the crank was rusty, all this caused by the loose backplate. Im just kinda pissed off cause this happened. I mean I never opened up this engine before and I trusted that the factory did a good job tightening the backplate screws enough, apparently not. O well i guees ill have to put some lock tite on the back plate screws and learn from this whole experience.