hi my 00 wr400 has run good for the past 2 years but now has started to back fire when im slowing down a lot , it has stop idle as well and is very hard to start . it runs good when driving at hi rpm but not so good at low . any ideas

Sounds like a blocked pilot jet or dirt in the fuel bowl.

+1 on the PJ. You should have a 45# or thereabouts in there. Either take it out and clean or if it were me, i'd pop a new one in there.

A problem with WR's.....go forever.

Check the valve clearances to keep everything tip-top. If the popping on decel persists, make sure you there are no leaks around the header.

thanks lads ill try that i was told it could be timeing chain so was geting worried there ill let u know if it works

.i put it up for sale and the day after it starts this i dont think it wants to go , THANKS LADS

Almost certainly nothing to do with the timing chain. I had a WR400 for two years with a rattling timing chain and it still ran fine. Unless it has jumped a tooth, but it doesn't sound like that from the symptoms you describe.

If it's not that Jet, my money's on one of the Exhaust vavles getting tight... check the valve clearances.

Maybe an inlet vacuum leak. That can cause backfiring.

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