After doing some reading about sparkplug fouling (reference to my 25hour
average life using 100LL), I believe that the combination of carbon core
suppression sparkplug wires AND a resistor sparkplug may be contributing to
their short effective life.  I just refitted my 13B with MAGNECOR Metallic
Inductance EMI Suppressed Conductors.  They seem to suppress any ignition
noise in the radio as well as the carbon core ones.

>From what I read, apparently the average inductive generated sparkplug pulse
takes approx 100nsec rise time.  If the sparkplug has carbon or lead fouling
coating the ceramic cone this tends to provide a lower resistance path for
the spark.  As the leading edge of this slow? rising pulse starts to build
the voltage is bled off by the lower resistance path which may prevent the
pulse from rising to a voltage level necessary to jump the electrode gap.

They used to make spark plugs that had a fairly large space gap in the
center electrode wire inside the porcelain part of the plug.  This prevented
any voltage from getting to the cone/center electrode and prevented the
"Bleed Off". Once the voltage build up sufficient to jump the space gap it
had more than enough voltage to jump the electrode gap at the firing end.
Also, this space gap apparently had the effect of causing the effective
duration of the pulse to decrease from 100nsec to approx 10nsec.  Due to
these effects these type sparkplugs were fairly effective in firing a fouled
plug, but alas apparently they are no longer made.

This may also be part of the reason that some of the CDI type ignitions are
more effective in firing fouled plugs (shorter pulse rise time which doesn't
permit as much voltage to be bled off and the voltage is higher to begin
with).

So will let you know if this improves the plug life.  Next is to get some no
resistor sparkplugs from the motorcycle shop and try them out.


Ed Anderson
Matthews, NC
RV-6A N494BW
eanderson@carolina.rr.com