just a guess but sounds like the needle on the carb needs adjustment if it has one, pull the throttle once it warms up a minute or two, and slowly turn the screw counter-clockwise until it runs better. At full throttle adjust it where it runs best. Then let it idle. If it dies adjust the idle faster which can be a stop screw or the cable tension. At idle pull the throttle somewhat quickly to see if it responds well. If it stumbles turn the screw just a tiny bit more counter-clockwise. Do that until it doesn't stumble when you open the throttle. On those engines the temperature outside, how long you use it, how much gas is in the tank, how old the carb or gas is all can affect how that machine will run. I sometimes carry a small screwdriver around when using one of that type engine to tweak it as needed if it doesn't like the day. STAY OUT OF THE WAY OF THE TINES WHEN YOU ARE WORKING ON IT.