I had a similar issue with my ride, when the load got too strong the engine would cutout, could rev all the way through the range if I did so gently but quick acceleration and the engine stumbled and fell flat. Turned out all 4 main jest fell out of my carbs so it ran too rich. I'd go through the carbs again and make sure you didnt forget anything or that nothing has gotten into the system since you cleaned it. Good luck

 

hahaha, and that is a 1 in whatever chance of all 4 doing that too Prom. When you mentioned that way back when, it floored me.

 

Cross my heart, lol. but yeah I doubt that happened to your bike but it is a similar result, could be running rich as well.