Hi Volture,
I have a few of these Poulan engines myself. I have two 21cc engines, 2 FL-25s and an extra jug and piston but no rings for the piston. Someone overheated the engine and cracked the rings but the piston and jug seem to be ok. The only reason to mention this jug and piston is because it has 2 rings and the piston diameter is between the 21s and 25s I have. I was surprised to see a Poulan with 2 rings. I might buy some rings and put them to use. The 21s at first only turned 6k so with nothing to lose I ported them and they now turn a 16x8 right at 7k. I got one of the 25s to turn the same prop 8200RPM. I will soon test the other 25 to see if I can duplicate the RPMs of the first one. I don't intend to mess with many more of these, but they are nice running engines for what they are. On the long shaft, with a Lathe, you can cut and rethread it. Doing it with a hand die set is tough to do accurately, as you can guess. (There is too many engines and not enough time.)