Hello chaps, I think my bike has started running rich but I don't know why. Nothing has changed since I got the bike in May. Under hard acceleration with over 50% throttle, usually in gear 3 or above, about half way up the rev range the bike hesitates, only slightly, but noticeable. It will be gaining speed then just die a little for a split second - same part of the rev range. It's not a flat spot - it's a fuelling glitch. The previous owner had put a K&N air filter in so I cleaned it and oiled it making sure I didn't over-oil it and changed the plug. Also, there is a sooty patch on my rear plastics by the exhaust exit. Also the plug is pretty black. I'm pretty sure the bike wasn't doing this when I got it. The only thing I can think that has changed is the air temperature but surely that wouldn't affect the fuelling this much? Any pointers as to where to start looking? It's a 2005 Honda XR400 by the way. Cheers.