I'm using a 25cc weed eater motor (poulan). After removing the plastic casing and pull start, I see the drive shaft. But there is a disc at the base of the drive shaft that spins with the shaft. It has a magnet piece that rotates by a little black box. The black box has the spark plug wire coming out of it. So is this disc a part of the pull start or is it necessary for the engine to run. Removing it would give me an extra needed inch of drive shaft.