If you ease into the throttle, the engine speed increases normally, but then the engine just suddenly cuts off at a certain speed, you might have an ignition problem.
If the engine will rev. with the choke on, then its probably the carb.
If the problem is the carb, it needs to be PROFESSIONALLY cleaned. - spray cleaners and $15 per gallon parts store cleaners are about as good as pouring water on it. You buy a 5 gallon starter bucket with a dip basket for about $75 to $125 (depending on your discount leve)l at a auto supply and about $45 a gallon to replenish what is lost during the cleaning process. Completely disassemble the carb, clean all the parts (except rubber parts), assemble and recalibrate and it should be as new.