1993 yamaha 225 txrr 2 stroke, sudden rpm loss

[Pursuit220C]

yamaha 225 txrr will loose rpm after 30-40 min. Runs great otherwise. Engine will drop to about 1500 rpm with the throttle in the same position as 3500 rpm. The engine if left alone will try to get back up to rpm on its own but doesn't. The engine then runs really rough at idle. You can throttle back up and achieve a desired rpm then it will drop once again. Fuel system has been gone through except for the primer pump on the engine (the one with the manual choke switch) will be testing this today.

Will and over temp sender do this to the engine without an alarm? Things don't seem to be overheating.

Very frustrating when the engine runs so strong then losses rpm and runs rough afterword. Any help would be great.