Hello I have a Gravely 8122, I’ve been having a problem where it’ll run fine for 20 minutes or so then it’ll start bogging down. As soon as I disengage the pto the engine goes back to normal but if I engage the pto then it starts bogging down again. I’ll turn it off for about 30 minutes or so and let it sit, then I’ll try to mow again and it does the same thing after about 20 minutes. Does anybody know what this could be??? New carb was just installed also but it was doing it before that too.