I have an engine from a gold pro duraforce that is extremely hard to start. I have replaced the coil and the carburetor with those from a know good, running lawnmower and it still won't start! the engine has 120psi of compression, and the reed valve seems to function correctly. What am I missing? The only way I have gotten it to run at all is with starting fluid, even then it seems "lethargic"- HELP!