You should do a pressure and vac test (cranckcase and carburetor). Also check your fuel and impulse hoses for cracks and leaks and replace them, also all filters. If possible do ultrasonic cleaning on the carburetor and make sure that after the cleaning everything is assembeld and tuned properly and the metering lever has it`s base setting. (depends on the carb) It would be good to replace all gaskets too. From your description it sounds that the engine is running to lean, which can have different causes. Don`t run it like this or you may score the engine. If you do the pressure and vac test you will find the leaks. You can spray soapy water on the seals while doing the pressure test. If there is a leakage you will see bubbles coming out.
Also check through the exhaust port if it is scored already. If yes, it`s a complete rebuild to do.