You can convert a Ryobi 31cc weedie for under $100 EASILY.

Call around to the local lawn mower--small engine--shops and see if they got an old one lying around that someone never came back to claim. Lots of times--it ends up costing more than they are worth to get them fixed. Most people will just leave it at the shop and buy a new one for $50. The small engine shop will be happy to sell ya one for $20 or less just to get it outta the way. He might even give it to ya if you tell him what your gonna do with it and promise to come back and show it to him when it's converted and installed on the plane.

Buy a carb rebuild kit from the small engine guy. They cost $12--$18 depending on the shop and the carb on that particular weedie. Rebuild the carb before you even try to start it.

As long as the piston and cylinder are in good shape---they are almost indestructable.

Buy a new ring from Frank Bowman in Farmington, NM. For a little added expense--you can convert it to electronic ignition. Call RCIGN1 a.k.a. Ralph Cunningham for the electronic ignition. VERY SWEAT setup.

If you want to keep the stock ignition system---but yours is broken--contact me. I've got a box full of Ryobi coils and magnetos

www.wackerengines.com for mufflers, mounts, hubs...etc..

On the 4*120--move the firewall back about 1" and look at putting some servos in the tail for balance.

Don't blow $400 on a 25cc Roto. DO A CONVERSION FOR $100!!!!!!! You'll be hooked for life.[:-]