Time for a leak down test. You checked the intake valve with carb cleaner but what about the exhaust? The symptoms could be caused by a burned or leaky exhaust valve. Listen to the exhaust pipe, the carb (with throttle open) and the crankcase vent when you have air in the cylinder. That will give you an idea of what is leaking if you have a problem.
"You can follow me, but it's gonna hurt"