Re: I hate 4 Strokes

[Don]

All I can say is that it seems like this engine has some sort of original defect that never got resolved. In these cases, we must make no assumptions, and remember to pay close attention to "the basics". I keep hearing references to the flywheel key, just seems like a sheared key would definitely affect valve and ignition timing. It is surely worth spending an hour or so checking timing belt orientation and the flywheel/key. How about the cam gear, perhaps it is improperly oriented on the camshaft/sheared key as well.
Again, you mentioned the engine ran for a few weeks, but how well did it run? Was it still tough to start? Did it idle properly?
You replaced the fuel pump and carb with new OEM items, correct? Did the engine run better/differently when these components were changed, even just briefly? Everyone has spoken about the small passages in these carbs, perhaps a dirty fuel supply has messed up this brand new carb….Doesn’t seem likely, but anything IS possible.
Try to avoid the temptation to "dig too deep", 95% of our engine problems are related to very basic issues. Trust me, I am not preaching, just trying to help you avoid the traps we all/me included create for ourselves…
This is an interesting project, wish I had more knowledge about these engines.. Look forward to finding the basic issue and getting it resolved.