how can i sort out my speedfight!?

hi i have a 02 speedfight and it goes 43-45mph on flat however goin into a tight corner i obvly have to break down to about 25mph and then coming out of the corner i try and accelerate and it just seems to be realy sluggish and slow getting to 33, from here it accelerates to 45 rapidly
its almost like its just the mid range has no go
can any1 help me

was thinking about putting a 1500 rpm torque spring and clutch springs on it will this help?????????