The timing " pick ups " move when you adjust timing, so you throw off the timing of the crank sensor compared to the cam sensor. Causes a hesitation mostly noticeable @ 2,500 rpms. There were some cam gears made that were basically stock ones modified to only move the outer part so the pick ups would remain in place... but they are limited, and rare, and not made anymore. The few that have them are very seldom to let go of them too.
