Originally Posted by MikeXray

Not big enough, are you running MM? I find mid allows a bigger pinion with the 70 range spur. For a quick fix I would just get a AE 72 or 69 spur and clamp the slipper down completely to run 17.5 (the plates are a bit too big so once the pads wear down some you end up in contact with the spur, not the pads). You want to be in the 69/30-33 range depending on track size, and most motors will run best with +20 or more timing (again depends on motor and how they mark it).