ok, so my buddy has a lawnboy that is about 3 years old, that won't start at all anymore. I took it home, cleaned the carb, air filter, etc. Basically all the easy stuff. And it still won't start. This mower is in GREAT condition, expect for the engine won't start. But I think that the rings are shot among others things. Nothing is wrong externally, its all internal. What do you guys think that it would cost to get this thing up and running again with just the brief explanation that I gave you?