Hello I have a Yamaha XT 125R And i can get 85 out of it flat out   
	Utterly Fazed
Is right in saying you need to bore out the outlet pipe like i did I will Put a list of mods i did to my bike to get it to achieve 85 mph 
  
Racing Carb 
1.20mm Main Yet 
4mm Bore outlet pipe 
Removed exhaust Baffles  
Put the Front and Rear suspension on the lowest setting  
  
I did just them without getting big bore Kits and sports cranks I spent £150 on the mods and got an extra 15-20 mph from it so its up to you how far you go with it  
Hope this helps