Flush the carburator with straight fuel through the fuiel line with the needle valve removed.  reset the highspeed needle and the mixture valve to factory defaults.  If you do not start adjusting the mixture valve from the default position you will never get the engine to run properly in all operating speeds.  you can have an engine run great with the mixture valve improperly set by having the needle set to work well at that one speed but as soon as you transition from that speed the engine will run like crap or die