my 06 Yz450 wont idle down unless I clutch it. It backfires on decel like a machine gun. The valves are within spec. Has a 4% leakdown. 45pj/165 main. The hot start is seating fully. It's not leaking at the carb mount. The exhaust dont have any leaks. It ran fine and I took it out to ride one time and it was doin this crap. I cleaned out the carb and it didnt help. Turnin the fuel screw does'nt help at all. I checked the entire electrical system and everything checks out fine unless it's intermittent. I dont know what else to check?