You have lots of patience. Thanks for posting the results. Classically, the best "weedie" performance gains are from a more free breathing exhaust, and from a larger carb. One won't work well without the other though; with the more open exhaust having an advantage if you are only going to change one thing usually. The next thing is to check the exhaust port timing. Some Ryobis have a really low exhaust timing of around 120 degrees. Bringing them up to about 150 really livens things up.

A good way to check your deck height without all the caliper work is to use a piece of solder. Bend a piece so that when inserted into the spark plug hole, it touches the side of the cylinder. Then turn the engine over a few times. The piston will smash the solder against the head, and then you can measure it for your "deck" or piston/head clearance. .015" is a minimum deck height, with maybe .020" being a bit safer or a good idea for high rpm engines.

AV8TOR