Andrew Rowley wrote:

(John Galban) wrote:


I think there's some confusion about your troubleshooting. In the
original post, I (possibly by mistake) assumed that when you switched
to the rough mag, the #2 EGT "shot off the scale" to the low end (i.e.
cold). If you're saying it shot off the high end of the scale, this
would not be the kind of reading you'd expect from a cylinder that is
not firing.


A weak spark rather than no spark maybe? If it's firing but less
efficiently?
My understanding is that this effect also causes EGTs go up when
running on only one mag.

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.


Matt