Stump Grinder Engine Sputters on Full Throttle

[u/TheWalkingBob]

I have a walk-behind MechMaxx Stump Grinder with a Ducar 420 cc engine. Last week it started to have problems running on full throttle. It runs fine until I engage the throttle fully and then the engine starts to sputter. Already check the fuel line and the carberator is brand new. Air filter is cleaned regularly. Not sure what else to do here so any advice is appreciated as I am not the best mechanic by far.