Ignition Problem (sorta related)

[Greg Hermann]

>Funny Gorden,
>
>That old trick still works in todays modern two stroke motocrossers.  We ride
>KTM big bores here in NM and sometimes because of altitudes we ride in the
>plug may sometimes foul.  I just reach up and remove the plug wire and set it
>on the plug and kick it few times, sometimes it fires sometimes I have to
>replace the plug.
>
>The coil only applies as much voltage as is required to jump the gap, and yes
>it will require a little more to jump two gaps.  The average coil in the end
>will only have so much on hand to meter out to jump the gaps, but within
>reason it will have ample voltage and current to jump a couple .060 gaps with
>relative ease.
>
>Tom Wong
        What's really going on here is that oil fouling on the plug is a
conductor of sorts. If the oil leaks current too fast (faster than the rise
rate of the coil can build voltage) the plug never fires. A second gap in
the secondary circuit (prior to the one where you want the fire) prevents
any charge from leaking across the fouled gap. When the spark jumps the
first gap, you get a much faster voltage rise across the one in the hole
than you would directly from the coil. "R' type plugs are built to do
exactly this full time. If you doubt me, buy an R type plug, break it, and
observe the gap in the center electrode! Yep, you get a lower voltage spark
across the gap in the hole, but the faster rise rate is often enough to
make it fire, even when it won't do so otherwise.
                                        Regards, Greg :)