I have an old plane that originally had a K&B sportster .20 on it. That engine worked great but I wanted more power. I had set the plane up with the crazy K&B engine mount that bolts on the back of the motor, so the sportster .28 seemed like a perfect and very easy solution. I've only run a few tanks on this motor, but the performance is pretty bad. Considerably less than the .20 version. I think it may have some carburetion issue. It's ornery to get the needle set right, and it seems like the last 1/3 or more of the throttle doesn't give my any more RPM. Any suggestions? This motor is pretty much unused. I've only run it a couple of flights and probably a half hour on the test stand.