I would just like to add that the O.S. engines are the most reliable I have ever ran. I've run a ROSSI, ABC Super Custom and the newest O.S. LA 65 and this engine is the tops. Good startup, great acceleration, and awesome cooling give O.S. engines a real step up from the rest. They are a hare more expensive, but you will have that engine running great for years with minor upkeep along with your trainer. However, I must note that if you are going to be flying in sport/competition, ignore my advice. All my experience is backyard, dirt, unimproved surface and concrete runways with trainers...nothing more. I have heard that other brand engines run better(more $$ for the engine purchase and fuel) when in competition; however for weekend flying try to stick with O.S. engines.. Also, If you are a beginnner or don't consider yourself intermediate just yet, keep the stock SIZE(brand can be changed depending on dry engine weight difference) that your aircraft is expecting... a 40 size engine for a 40 size aircraft(60 for 60 etc..). When you do this, and ideal balance(stock location of C/G or C/B), the aircraft will better handle a little extra weight for accessories(night lighting, cameras, and my favorite the candy bomb bay etc). Now, Take Off!
Safety: First, Last, Always.