06 yz450 backfire and idle problems

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?

This really sounds like a cold air leak, like maybe the carb boot or somwhere in the exhaust, but if you checked that all.....maybe its a problem within the ignition box...

I had this problem when I had water in my gas:banghead: :worthy:

When you said you cleaned out the carb did you remove the slide? If so you want to make sure you put the small plate on the slide on right or else it will do exactly what your talking about. I had this exact thing happen to me when I removed my slide.

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