putting knobby tires on it

Anyone had any experience in running knobby tires on the Suzuki Fa 50 Shuttle scooter? (I know I would have to raise the fenders away from the knobby tires to avoid tires rubbing on the fenders). The problem right now with those original tires not being not knobby tires, is that on the rainy and thus muddy days the original tires pick up all kinds of leaves and sticks that get packed in the fender, making noise and slowing the speed down, especially the rear fender where there is that indentation in the fender for the carburator's air breather hose clearance.