I have a 2000 20 hp Mercury outboard which I purchased several years ago and I never ran. The engine had seen occasionally seasonal use with no problems and was sold when the owner upgraded to a larger boat and engine. The engine had been serviced and winterized by a Mercury dealer just prior to my purchase. I mixed fresh fuel with Mercury outboard oil, and managed to get the engine running by manually opening the throttle linkage about 3/4 of and inch. It ran very rough. By removing the spark plugs I determined only the upper cylinder was firing. I did rotate the ignition coils and plugs (new plugs) and it still only fires on the top cylinder. Any suggestions?
