the things mentioned above, some other things to check ( I presume its still running on the 17 inch supermoto wheels by the way) Wheel alignment, although there are usually marks on the swinging arm and adjusters to keep rear wheel aligned correctly these are not always 100% accurate, a straight edge (long piece of wood/spirit level/ length of angle iron) can be used to confirm alignment, when it is touching one side of rear tyre at front and rear, then when bars are straight front wheel should be in line with this, allowing for thinner front tyre. Are tyre pressures correct, you may able to lower it slightly due to lighter weight? Are you sitting at front of seat, this is quite important due to bolt upright seating position, easy to slip back due to acceleration and flat seat! It possible the forks may need the pressure released, long travel forks like those can pump up after a while, may be bleed screws to loosen on top of forks (may also be damping adjuster there too) If there are damping adjusters, you may be able to back those off a little, especially the compresssion adjusters. As m1ks says they are a little more skittish than a heavier bike, and less stable at speed, although it shouldn't get out of hand!