Wow, you replaced a lot of parts! Hope you saved the old carb.
It's a sticking exhaust valve.
Need to pull the head, take the valves out, de-carbon everything, plane the head, clean the valves and guides, and put it back together. Valve job would be in order too if it was my machine.
If you question my diagnosis, you can confirm by getting it to act up, then taking it inside, pulling the plug and using a blow gun (with a rubber tip) on an air compressor to put a little pressure in the cylinder through the plug hole. You should hear air coming out the exhaust even if you roll the motor.
Note: DO NOT roll the engine by hand while putting air pressure in the cylinder. It may turn on it's own, and hurt you. Stop the air to roll the engine.