Stars and runs no prob. splutters and stutters in

First thing check the gas flow to the carb, next check and clean the jets, If it is starting and sound ok the idle jet is working but if under load it sputters it is possible main jet is not working well, Also you could have an air leak check all gaskets on intake side, Last of all you could have a leaky head gasket check compression, under load it could **** air through the head gasket causing inmproper combustion and it will sputter.

If this is something that just started, I'd check the spark plug and ignitions system first. Then move to the air filter and carburetor. Check the silencer in the pipe to see if it's clogged up.