Reply To: Mercury KF-7 lightning – bottom cylinder drops out.

[billw]

My two thoughts would be either the bottom cylinder is ingesting a bit of water from a bad lower crank seal or inner exhaust plate, or maybe if it has had a new lower crank seal, one was installed without the tiny drain hole in the seal’s case, as was often seen in that vintage of 20 cube Mercury? That would mean the bottom cylinder couldn’t get rid of its puddled fuel correctly. Dave’s ground wire idea is sure an easy test, though, before you get any deeper.

Long live American manufacturing!