If you have the carbs. cleaned and adjusted right you should have no problem getting that bike up to 70mph.You might be having slipperage in the clutch area,check to make sure your clutch is not slipping.That is one thing that will not let the bike get up to speed,try adjusting it on the end of the clutch cable down on the right side of motor.RIDE IT LIKE YOU STOLE IT IN ALABAMA.