This is why we do runups

Pat Barry wrote in message ...
Dear John:

Mechanically and technically, and while I'm not doubting your post and your experience with plugs,
this makes no sense.

If plugs are cleaned and gapped there is just no cause attributable to plugs that would lead to extra
fouling. If, however, the plugs had worn to the level where the electrodes are spaced too far apart I
can see where the uneven spark would cause uneven combustion which, in turn, would cause lead
fouling.

I'm racking my brain to think where time in service would make a difference - and the only conclusion
is mechanical failure, possibly a cracked ceramic area of some type of wear, if other than the
electrode gap?

While I don't have any specific data, I've always assumed that it's
some type of wear. I generally get about 700 hrs. out of a set of
plugs. That's about the point where the electrodes start taking on a
football shape. When replaced with brand new plugs, I always noticed
that the propensity for fouling decreased. Upon reading your post, I
see you're point. As the plugs aged, one or more may have had some
sort of mechanical problem that caused a weaker spark (as evidenced by
the increased fouling).

John Galban=====N4BQ (PA28-180)