WHILE IT IS RUNNING, TRY PULLING THE CHOKE OUT A LITTLE AND SEE IF THIS HELPS.
IF IT DOES, THEN THE CARB NEEDS CLEANED.
THERE SHOULD ALSO BE A SCREW DOWN CLOSE TO THE FUEL BOWL IN THE CARB BODY.THIS ONE IS JUST A DRAIN FOR THE FUEL. I HAVE DRAINED IT BEFORE WITH LIMITED SUCCESS, BUT WORTH A TRY.