The dead sticking at high power settings could be a lean setting of the high-speed needle. The high speed needle should be leaned out at full throttle until the enging "peaks", then backed-off (richened) until you just hear a small drop in RPM.

Conversely, at idle, it sounds like the low speed setting is rich -- the cranckcase is loading up with fuel & eventually the engine floods out.

The high-speed needle must be correctly set before you start adjusting the low speed needle. The LSN is adjusted by turning the screw inside the center of the throttle arm assembly, located on the right side of the carb --- look in the end of the throttle barrel & you will see it. Make adjustments in 1/8 - 1/4 turn increments. Turning it clockwise leans the low speed mixture & turning it anti-clockwise richens it.


Once you have the low speed needle adjusted satisfactorily, the engine will idle reliably for an extended period & accelerate to full power without stumbling or stopping.