to free it up alcohol or raw fuel squirted in the intake and exhaust and rotated should loosen it up enough to run,there are no ball bearings to go bad and it is not an abc design,upto the fp 35 were lapped piston designs,I think the starting with the 40 they used a ring.reqardless of the above post the fp series are a good engine,they use an airbleed carb instead of the two needle style found on the fsr and sf series.fp[flat piston] were the economy model schnurle ported engines for sport/beginner flyers.I think some of the older os engines were made better than todays engines,no plastic parts to break,you should use a fuel with a bit more oil content than 18%,20-22% is what they were designed to use.