okay, so here is what we know now:
manually giving the engine more and less air made no difference.
that leads me to believe the issue is not related to the carb or fuel.
it sounds like the unit is loosing spark once the engine rpm speeds up.
you ave visually checked the woodriff key that keeps the flywheel lined up with crankshaft?
next you should check the pickup sensors, also known as the pulse coils. do you know where they are on your unit? (behind flywheel cover)
you will need to unplug it from the wire harness, then use a multimeter on volts AC, and put the leads from the meter on each wire.(the pulse sensor is 2 wires for each one, usually blue and black). so one meter lead on one pulse wire, and the other meter lead on other. it does not matter which lead hooked up to which wire.
with meter hooked up, use engine starter button to make engine try to stat (it will not start with this sensor unplugged-you are only testing signaling output of sensor).
with engine spinning over, the pickup coils should put out AT LEAST 1.2 volt AC.
do tis test. if you need better instruction, let me know.