Not up on my reg plate numbers but that sounds newer than the 04/05 models which had a faultly ECU. They where replaced by yamaha but some people did find you had to fight a bit to get the work done.

Anyway normally the way i describe the surging of the XTR is that at a certain set speed and gear its like yamaha (or the emissions police) have tried to make the bike cut the fuelling (as you say stravation) even though you might be asking the bike to do part throttle stuff. But the only thing is being a big single your part throttle and them trying to cut the fuel mean in stead of the engine feeling as if its dieing or straving of fuel and leaving you with an on off throttle theyve tried to get round that and it can jump where its like on off on off throttle even though your keeping the throttle the same. Basically like the engines trying to pick up and then lets go again.

Sometimes its not a problem as if your on a road no one else around you either speed up, slow down or flick another gear. But mid corner, traffic, or people are just travelling at that speed where it happens can be a bit of pain.

But as you said most riders have got use to it and ride round it, most with out even knowing after having the bike for a while.

Be careful as the same effects on the XT can be felt by having a loose chain or the cush drive rubbers being worn (wear out quiet quickly on the XT due to the torque aka wheelie fun).

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Plough on