the x1100c will never be a speed performer but there are some things you can do to get it to it's best. 31 inch tires are going to probably cost you some performance but 26 inch tires seem to be about the perfect fit. run the tires aired up to 20 psi will help also. run super udtII oil in the transmission and change it often. the hst speed lever is very very dependent on it's relationship with the throttle speed lever on the injection pump and the travel on the foot feed. the x1100c was derated jut a bit to keep it in the clean air spec so just a little adjustment to the fuel screw and a slight increase in rpm will get you to 25mph and also help with power in all speeds. the settings on these run from horrendous to pretty close from machine to machine and the service manual is written in a strange form of english that makes a simple adjustment hard to understand.