I have used this engine for over one year and it has been super reliable, one of 4 OS's I have. Yesterday it would not start. Glow plug ok, fuel lines ok, removed head to see if cracked or dirty, but the engine when finger flipped will only softly pop once and not run out the prime or other fuel. It also feels as if compression is down somewhat, especially compared to the other OS engines. I am at a loss as to what to do. Help