Charlie reminds me:Â* I had a new Ford pickup back in the 80s and, while
still under warranty, it started running roughly.Â* The dealer was unable
to find a problem until they closed the roll up door on their garage and
then, in the reduced light, they could see one of the spark plug wires
arcing to the engine block.

Maybe replacing the spark plug wires is also a good idea.

On 3/30/2020 1:36 PM, Charlie M. (UH & 002 owner/pilot) wrote:
Plugs (I use NGK copper/V power) or wires/coils. A COP or extended plug wire into a well....look for carbon tracks from spark wire to ground....most noticeable at higher combustion loads (higher RPM's in NA, higher boosted in SC/turbo engines)....HV charge goes easiest path....higher combustion pressure sorta insulates spark going across plug gap....spark goes easy way....
Damp ignition can make misfires....so a damp day can make issues vs. a dry day....
Dielectric insulation of ambient air at seal level, standard pressure, is a lot lower than high compression/high load NA or "force fed"..
Physics son.....physics.....

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Dan, 5J