Bryan and Art,
I'll take the opportunity to chime in on the subject of ignition noise and why Tiny Tachs don't work very well on Kohlers with battery ignition systems. Ignition coil is an inductor (current storage device) hooked to a capacitor (voltage storage device). It's the basis for an oscillator circuit. When breaker points open collapsing the primary field in the coil, an outrush of stored current occurs through the coil primary-breaker point circuit. The voltage can be as high as 250 V due to the turns ratio in the coil. Its known as back EMF (electromotive force). The capacitor is there to protect the points from this 250 volt EMF arking across the contacts, which would erode them in short order. The condenser momentarily stores the energy but acts like a spring, sending current back to the coil. The coil then rebounds sending it back to the condenser again. This "ringing" of electrical energy is disipated after a few cycles but it is enough to throw an inductive tach into a frenzy.
Now a comment on transistorized ignition systems used with breaker points (perfect opportunity). By eliminating mechanical contacts handling this back EMF and using a semiconductor instead, the condenser can be eliminated entirely as the transistor (properly selected) can handle switching this electrical energy with ease. The breaker points now only handle the current necessary to turn the transistor on and off, and this amounts to about one hundredth of the amount of current in the original circuit. As the coil is instantly and rapidly turned off when the transistor opens, no more voltage absorbtion from a capacitor occurs, therefore more energy is imparted in the coil secondary winding (hotter spark) and no circuit ringing occurs. The Tiny Tach should function perfectly without alteration on a transistorized ignition system (I haven't tried it yet but in theory, it should).
I'm sure those guys that are electrical experts could explain all of this better than I and if so, please help.
(Message edited by dkirk on January 19, 2004)