You can't go wrong cleaning it up inside. Do just exactly what you described. Take off the flash and match the cylinder transfer ports to the case. Clean up the case/cylinder gasket to prevent any disturbance in the flow.

I've done it with some of the little conversion engines and even did it once with a Poulan 54cc conversion. I did notice a few more RPMs, but nothing to brag about. Maybe 100RPM. I thought the Poulan 54 idled smoother after I cleaned up the case to transfer ports and matched them up. I didn't really take off that much material. I just knocked off the dog ears here and there and used some fine paper to smooth it up a little bit where I worked it with the dremel.

The really cool thing about the Poulan 54 was it had a split case. I bolted 1/2 the case to the cylinder and matched the ports exactly. Then took that side of the case off and bolted the other side onto the cylinder. Cleaned up that side and polished it just a little. When it was all done--I had the match between the case and the cylinder just about dead on.

My friend and I have done things to the twin ring Ryobi 31cc engines that you can't imagine. The mods work, but that little engine has such a week rod, it can't take much hopping up. We didn't put enough prop on it and the engine let go after about 2hrs run time at 8800RPM. Just bumping the compression by lowering the cylinder does a lot. Then bring the exhaust port back up to stock and maybe a little more. Slap a bigger carb on it and bend the reed stop out a bit. We started running high octane pump gas. 91 octane and 40:1 mix. It works, but you really don't want to take them past 7500--7800RPM on the bench. We had one turning 8800RPM with an 18" prop. It broke after 8 flights on the Lanier Stinger 120. [sm=confused_smile.gif]