jetted to high, try get it checked out at your shop as you may not have the knowledge to adjust the jetting setting, either that or carbys filling up with gunk, fouling spark plus or dodgey fuel. use recomended fuel by the manual
high revs, and it splutters and coughs... your either outstripping the fuel supply, (check for a kinked pipe, or other bockage in the carb... or the air filter is blocked...
engines need to breathe... oh, and they also need to exhaust, or they choke up, and die...