A O.S. 91 Does the Job for the UCD
I have a .91 fx 2-stoke on mine, and I am using an APC 14 x 6. It pulls it real well, and has unlimited vertical. I tried a 15 x 4 W, and did not like it at all. The engine just didn't have enough torque, and was very sluggish and slow to spool up.
DK