If someone else had access to the tank then I for one would be having a very serious discussion with that individual right now. >:

On the other hand, someone may very well be playing a (not so funny) practical joke on you.
Check the seal of the fuel tank cap for sugar granuals that may not have dissolved, if none are found then I doubt anyone put sugar in your tank.

If someone actually did put sugar in your tank, then you would know it after less than 20 miles of riding which would be followed by a call for a tow truck.

As far as fuel filters go... I looked in the service manual and found no mention of them... but that doesn't mean they don't exist... call your local Yamaha service department and ask.

Good luck either way.

>: Yeesh, people like that really tick me off. >: