Well, assuming nothing is defective....
Excessive Arching is usually caused by not enough spring tension....try increasing the tension of your springs. Most p2ks work well with trinity red on the positive and green on the negative...
Trinity springs in order of stiffness (stiffest first)
Now, if that doesn't work....more than likely something is defective in the motor, which could be a burnt winding, blown capacitor, etc....