start with fuel, fire, and air 
back your idle screw all the way out, and put your air screw all the way in - then back in out about 1.5 turns. drain your float bowl and see what the fuel looks like - pull your plug and try dry firing it by grounding it on the case when you pull start it. try starting it up again, give her a little throttle if shes stubborn (try choke)
if you have to give it throttle to keep it running and it seems like the carb is tuned then you can turn your idle screw in a bit to keep it running.
check that stuff VM said (except for the valves, hes crazy) surely the valve adjustment isnt way off
LOL whats up VM!
you think when the valve seats get worn enough it affects the adjustment? hmm..
quiet people seem intelligent