I was hoping someone might be able to point us in the right direction. We purchased a non running GN250. After first inspection we noticed that an exhaust valve had blown and had damaged the piston. So we replaced both parts and hoped that this was the solution to the non running engine. It wasn't! It has spark, it has fuel, we have also used easy start and it has caught fire but no explosion for piston to start (newbie description), we did use gasket sealant and now are thinking it must be compression issues. When the engine is built and a finger is placed over the spark plug hole there is a slight amount of pressure but not enough to blow the finger off. Our thinking is to replace all the valves as some look burnt and possibly not creating an effective seal and replace all gaskets. Next move? Any advice appreciated!?