If the engine turns over smoothly when you remove the glow plug, except for a slight tightness at Top Dead Center, then the engine should be good. If it's hard to turn over even with the plug removed, you may have a bent connecting rod.

Sometimes, a lean run or dirt can cause problems with the bushing...dirt or overheating can cause a bad fit....the engine will then tno turn easily. A new case, and sometimes a crank may be needed. However, at the costs to replace those items, you may as well purchase a new engine.

Generally, if an engine has good compression, good fuel, and a good glow plug, it will fire. If the carb's clean and the fuel can flow freely, then it should run once it starts.

Your O.S. Max .46 LA shoudl be able to be started with teh high-speed needle opened to about 2-1/2 turns out from closed. The air-bleed screw shold be set so that one-half of the airbleed hole is obstructed by the screw. Lightlly choke the engine and start it at 1/4-1/3 throttle.

If the engine's particulary hard to turn over, then something's broken or bent.