pull the rocker cover off and see if it any push rods have fallen off the rocker arm. i remember that happened to mine once and i was running on 2 cylinders for like 5 or so hours then teddy from ke70.com and a few other guys fixed it on a cruise with eye feeler guages and cleaned the metal out of the oil from the rocker cover being belted with straw...

apparently it happens a fair bit with 4ks too.