I put the 27" mudlites on my Rincon. I can only get to as fast as 75 km. Is a jet kit going to help me out or is that the best it will do now. It only did about 90 kms with the stock tires

 

A dyno jet kit will only help on the low end. You added quite a bit of weight with those tires (compaired to stock). I would do a K&N, DynoJet Kit and Exhaust to get the performance you need. It will be on the low end but at least you will have more torque...