07 WR450 Have an intermittent issue with my bike. Generally runs fine then it goes into backfiring on deceleration towards the low rpm range, then it won't idle, just cuts out when you pull the clutch in.. I can turn the idle screw 1 1/2 turns and it will idle fine but still back fire. Then all of a sudden things change, the idle ramps up high and the backfiring stops. I turn the idle back down the 1 1/2 turns till it idles low again and it runs fine just like it should. It does not matter if it is at running temp or stone cold. Yesterday I road 20 miles just fine then acted up in last mile. Today it acted bad for the full 30 miles. I did change the plug, disconnected the fuel mixture sensor and neither helped. I'm putting in a new battery tomorrow because the conductivity is poor but it still puts out 12.8 v under a load. It is the original battery. Any ideas?