Well, I got it all back together, but this time with the larger crankcase, the long shaft crankshaft that balanced well, and the good reed valve setup. Before, besides the vibration the best it would do was 7200 rpms with an 18 x 6 prop. Now, it turns the same prop a surprising 8500 rpms. Looks like I better "prop it up" a bit. I am pleasantly surprised. It also doesn't vibrate now, as was expected. The short shaft I have that is out of balance is not out of balance just a little bit, it is WAY out. Some day I'll have to go through my box of old flywheels and see if I can find the one that came on that engine and see how it is balanced.

As far as mods on this one:

Base gasket left out and sealed with Yamabond (Lowers cylinder about .035" )
Exhaust port raised to provide a timing of 152 degrees
11mm carb
Dual outlet after market muffler
CDI ignition set at 28 degrees
Good style reed assembly with reed stop set to 1/8"

farley9n Yes, I still have that cylinder. I bought an extra Ryobi ring from Frank Bowman, and if/when my brother can find me another donor engine with the good style backplate and a useable piston, I am going to build an engine using that cylinder. It will be interesting to see how it runs. I haven't cc'd it to see what the compression difference is, but that cylinder has a larger, almost full hemi style combustion chamber in comparison to all my other Ryobi cylinders. I have a couple of good crankcases, bearing sets, cranks, and cylinders here; just don't have a piston/rod nor a good reed/backplate.... []

AV8TOR