I have a 99 WR400 that has been super reliable since I bought it new. It does not get a lot of use, probably 200 km's each summer. Last year it ran great as always, starts on first kick when warm, first or second when cold. I always run the gas out of the carb every summer end, change oil, etc before putting it to bed for the winter. This summer, the bike starts fine but it will not idle unless the choke is pulled. When I push the choke in it will drop to idle, stumble and die. It runs great if I keep the revs up, but it now pops on decel (going down a hill especially). Not sure where I should start looking? Pilot jet?