Bike is stock except V&H slip-ons. Been doing the servicing myself, since new, in accordance with the manual. Lately it's been running a bit rough, like a halting/missing sensation which makes the bike quite "jerky" to ride. Doesn't really happen in 1st when accelerating away from a stop. It occurs mainly in 2nd & 3rd gear in town riding at speeds of about 25-35mph at steady revs. It disappears when you wind the throttle open and, it doesn't seem to happen at all in 4th & 5th out on the roads when you're giving it plenty. There is also a wee bit of backfire that wasn't the case before. It's not me lugging the engine with too low revs - I know how these bikes like to be revved... It's not bad petrol as I've filled up (from nearly empty) about 7 or 8 times since this started. I don't detect any sign of exhaust leaks. Is this some kind of fuelling issue? Any ideas?