Gearbuilder, what's your budget?
sCREamnClones, the kind of motors that Ted is talking about start around $800, or less. Sure back in the day, brand new they might have been $5000, but those days are well gone. To judge the capability of 100cc motors by the KT100 is a disservice to them. It's possibly the worst POS 100cc two cycle made in terms of power and parity, yet its the most popular.
CR125 is another option, but then you have to get different gears, possibly fab up a shifter arm, deal with a MUCH heavier motor, add a radiator. etc etc.