I believe this is possible due to the fact that having both sparks allows
the mixture to burn more quickly and thoroughly prior to opening of the
exhaust valve. If the valve opens while the mixture is only partially
combusted, a jet of flame will exit the exhaust port. This can greatly
increase the EGT, while at the same time lowering the CHT as the same
amount of heat is produced from the charge, but more of it is going out
the exhaust pipe rather than being used to perform work in the cylinder.

Thanks, Matt -- I believe that's exactly what was happening when the EGTs
went off the scale (hotter), and the CHTs dropped down into the 200s.

I didn't have time to work on the plane today, but I'm gonna yank that plug
and have my mechanic test it in his brand new spark plug tester -- the kind
that actually pressurizes (or does it lower the pressure?) it while testing.

If that's not it, I'm betting on the wiring harness.

Thanks to all who chipped in -- man, that EDM-700 is an awesome
trouble-shooting tool.
--
Jay Honeck
Iowa City, IA
Pathfinder N56993
www.AlexisParkInn.com
"Your Aviation Destination"