My 2004 Yamaha 1100 vstar just suddenly started spitting and sputtering the bike has 20000km on it it always worked great until today can anybody give me any ideas thank you?

have yu ever adjusted your valves?? mine had 20k on it & started to misfire.dealer charges $200. seat comes off, tank, air fiter, cam covers.yu can lookit up online.replace the plugs while you at it.Type your answer here...