ST 16 ENGINE PROBLEMS

Well, you guys solved many problems for me and i now have another one that is driving me nuts. I have this tec oh16 that i just cant get to run. I have rebuilt the carb and tried two others and all do the same thing.The engine will not run without half choke. It will run for a few minutes and die. It seems to backfire thru the carb as well. I have set the valves, changed plugs. It has great compression and does not burn oil. the fuel pump works and fuel filter is new. I now believe I may have engine problem rather than carb. Anyone have ideas i would appreciate them,

Rebuild fuel pump --- don't assume just because it is "pumping" some fuel, that it fully works.  Make sure fuel valve is not clogged, and is open.  Replace all fuel hoses.  Make sure crankcase vent port next to governor is not clogged.  That should do it (this assumes nobody previously took the engine apart, reassembled wrong, and it is mis-timed).  Don't just do portions of an engine restore, do the whole monty, take the head off and inspect, etc.  Get the engine gasket kit, and do it all, including oil seals, if they are not leaking now, they will soon...