Thanks for your replies guys. Yesterday was my first proper ride since buying the bike from a Yamaha dealership, it was delivered by van, so other than a 6 mile round trip to the pipe benders with the stock exhaust on the bike, to be measured up for a link pipe, that was my total experience of it. I'd overhauled the exup valve as soon as it was delivered, finding no problems at all. I refitted the stock exhaust this morning and noticed an improvement but not what I'd consider acceptable. The previous, and first owner, had only averaged around 500 miles annually over the last 5 years and the dealership have suggested that running several tankfuls of fresh petrol through it could be the answer. So basically their advice is to get out and use it and re-evaluate the situation when I've put some miles on it. It is covered by a warranty, and am aware of the pitfalls of stale fuel. The throttle response is spot on when started from cold and the choke is on.