Mysterious Misfiring

There are many causes for intermittent misfiring from your engine. Recently, I experienced two that, in my opinion, were rather unique.

The break shown in the picture has been greatly exaggerated for clarity (I had to glue it back together when I exaggerated it too much!).

The first happened this spring while out for a sunny day’s cruise. Without warning, my bike suddenly lost power and didn’t want to keep running without constant blipping of the throttle. For ten minutes this would continue, when as suddenly as it had started, everything returned back to normal. Several days and a couple of hundred kilometers later, I finally made it to Ottawa HD for them to have a look. What they found was that the (less than 8000 km) Screaming Eagle coil had developed a near invisible crack in its housing (see photo) creating an intermittent arcing condition. Unless you were looking for it, it was unlikely you would see it. How that crack became is open to speculation, but I do know that it showed no sign of any impact.

The second incident occurred barely a month later. I was returning from Port Dover when once again my engine began to misfire. Each time I approached about 120 kph, the engine started skipping beats and had difficulty going any faster. When I did get past that speed barrier, it would accelerate, but not as well as it should. Instinctively, I started looking for loose wires but found nothing amiss. I did note later that when the engine was still cool, it ran fine. But as it got hotter, the problem would begin and intensify. For a second time, with careful throttle management I made it back to Ottawa HD. This time the problem was traced to the S.E. plugs. The insulator on one had developed the ability to spin once hot. How many spark plugs have you seen fail like this?

Both these failures probably can be attributed to bad luck. And if you should ever experience the same kind of luck yourself; at least you won’t hear the immortal words “never seen that happen before” at Ottawa HD.