well, back in my punker days i did this to my car.
run the hose from your windshield washer pump to a small hole drilled into your exhaust
fill your windshield washer fluid resevoir with oil from your last oil change.
VIOLA! push botton smoke screen. i used to circle steak and shake late night while holding the button down until i couldnt see where i was going
maybe you can rig up a similar device to you moped.