if the price is $75 and the kit is higher, and you get an engine with it and it looks well built, its a no brainer. Buy it, fly it when your ready, and if the engine doesn't work well, pitch it and get a new one. You can get a new engine for $50. Don't waste time trying to re-build it. I think you will find that the engine will run just fine. They don't always have a lot of compression. Just depends on the engine. I bought one at a shop one time like that and it was the best plane I ever owned. The engine was almost worn out, but boy did it run good!