Listening For That Awful Misfire—50 Ways To Get It Wrong

During the winter of 1971, English rider Cliff Carr wrote to tell me he would come to the US to race my Kawasaki 500cc H1R triple in AMA and other events. Because that bike was originally delivered with a heavy coil-and-battery ignition with mechanical contact breakers, Carr said he would bring with him one of the new German Krober magneto/CDI ignitions. And a Krober electric tachometer.

Little did we know that a problem lurked within.

The system came in pieces with installation instructions. I machined a taper in its rotor carrier to fit the left-hand end of the crank. I made up an aluminum adaptor plate to mount the three-lobed stator onto the crankcase. Three electronics boxes came with pantograph-like rubber mounting legs. Lots of wiring. It must have saved 20 pounds over the stock system, and once in place it made promising blue sparks across the plug electrodes. Lovely.

With its new Krober, our bike could be started by pulling through the rear wheel in second gear sitting on its rear stand.

That year we had a formidable opponent: New Zealander Ginger Molloy, who in 1970 had come second in the 500cc Grand Prix world championship on a Kawasaki. Ginger was a seasoned professional racer, secretive, close-mouthed, and tucked in through corners as if all bikes were 125s. He was after what in 2019 seems a pitiful amount of money: $6,000 of Kawasaki contingency to be paid to the season’s end high-point man in the East Coast AAMRR race series. Cliff and I wanted that money too.

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At one Danville, Virginia, event (they call it “VIR” now), Cliff was well positioned to win the 500cc race when his engine began to make occasional pops that got worse until the engine quit. This was the result of a misfire’s dumping unburned charge into one of the pipes, to be ignited at the next firing of the same cylinder 0.007 second later. The misfire, I would learn, came about as the Krober’s charging rectifier diodes (capacitors in a CDI have to be charged with DC, not the AC produced by the system) became overheated under the ignition cover. Solid-state electronics become flaky near boiling-water temperature.

This was a time of rapid development in motorcycle ignitions; mechanical contact-breaker magnetos were no longer up to the work. Femsa in Spain had developed an alternative in 1969, and that same year at Daytona, Yamaha tested two different types of magneto/CDI. In the spring of 1971, Kawasaki offered its H1RA kit, which included an advance-retard magneto/CDI. We bought one, but in testing at Loudon it became extremely hot (just after shutdown, I licked my finger before touching the rotor; my finger bounced from the explosive conversion of moisture to steam!).

Next time we tried to start the bike, the high-impedance starting windings were open-circuited (the six coils of the stator were not epoxy-potted, so engine vibration soon caused internal shorts from wire-to-wire chafing). A friend with electronics skills built an ignition tester out of a carpenter’s router. In one test, smoke appeared from the stator and an oscilloscope display showed that the ignition timing had simultaneously advanced itself. That explained a number of engine seizures. At nationals, we could see the official team bikes being pushed by as many as five men, popping weakly until they reluctantly started. At the end of that season, Yvon Duhamel’s mechanic, Steve Whitelock, showed me their boxful of dead stators.

That made the Krober's fast, effortless starting attractive, but hot weather and pop-pop-popping had already lost us one race. Our new drill was to fill a cooler with motel ice every morning and make cold compresses to be applied to the stator the instant the bike came in from practice. Whip off the fairing, pull the ignition cover, and ice down that unit! I had now provided holes in the ignition cover for cooling air and had mounted it on spacers to provide even more air access. In photos of team 500s from this period, you will see similar measures, including cooling scoops.

Later, a definitive fix came from Krober: A new system in which the heat-sensitive rectifier diodes were relocated from the stator to the three remote electronics boxes. The generating coils inside the three-lobed stator were already nicely potted, so wire chafing was never a problem. In the future, I would mount Krober stators on insulating phenolic plastic laminate rather than metal mounting plates.

Yamaha would shortly equip its 250cc and 350cc production racers with magnetically triggered CDI/magnetos. They weren’t perfectly reliable but they were a big improvement over 1902-vintage contact-breaker magnetos. After that 1969–’74 period of transition, motorcycle electronic ignitions, having adapted to the heat and vibration, were ready to serve reliably.

And what about that $6,000? Cliff and Ginger battled it out despite the ignition and crankshaft failures both suffered. In the end, Cliff collected the check.