[ruredy]

Are the rpms lower than when you first got it? sorry this is one of those "duh" things on my part. I can tell if the engines not running up to speed because i've been around so many of them.
check the pcv hose going to the crankcase from the air filter box, make sure nothings wrong with it.
If the cart is lifted then filling the oil to the mark on the dip stick will be to much oil and it'll probably burn some. burning oil will foul the plugs. If it did suck in oil there will be some in the muffle that'll have to burn off. A compression test would give helpful info if you do it right (most people don't) the service manual tells the proper way. all manuals are in the tech section

It shouldn't take much to engage the clutch, i've seen them stick open before, maybe rap on it with a dead blow mallet some might free it up. I use my hand instead to free them up to give you an idea of how much force it takes to free them, most of the time it works. what i'm trying to say is don't beat the **** out of it with a hammer. you could always take the cover off and clean /inspect it.