I rebuilt my daughters LT80 this winter. Everything except splitting the cases was done (top end, shaved head, clutch mods, boyesen reed, boiled/cleaned carb, powder coated everything, etc...)

After break in, it would cut out and even die at full throttle. At 0%-80% throttle it would run like a champ. You peg it at full throttle, it would go to an idle instantly, no sputter, no hesitation AND you could let off the throttle back to 80% and the engine would roar back to life.

I discovered what it was for anyone who has the same problem....
I put a small clamp on uni filter on the end of a hose to the carb vent to help avoid the typical dirty carb issues. The carb vent line had somehow become pinched and there was no venting at the carb. As soon as the vent could breathe again, it run great through the entire throttle.

So, if you have similar issue, check to see if the carb vent is blocked.

 

Sweet LT!
I did that filter mistake years ago. The boy was racing at Echeconne (Macon Ga.)zoom-slow-zoom-slow.It cost him a place.
Glad you shared.