The number of cylinders is just the scale factor - it counts the pulses from the coil, and depending on how it's scaled it divides by 2, 4, 6 or 8 to equal one revolution. Ground one of the posts on your tach and hook a lead to your negative post on the coil and touch it to the other post with the engine running. It will either be right or off by a proportional scale factor, 1/4, 1/2 or 3/4 speed.