Ok I've been working on a 1975 75hp evinrude. One cyl. #3 has shown signes of not running. it's been sitting for sometime. so I started out cleaning carb's, lines, fuel filter and change all three spark plugs. no change. I was using a timing light to check and see if the coil was working and acording to the light it was. Later I found out the that there wasn't enough juices to fire the plug. I replaced the coil and in the test tank it seemed to be firing on all 3 cyl. yet when I luanch the boat into the lake the engine seems to intermitingly fire on all 3 cyl. It realy feels like not enough fuel. recover the boat bring it back home and inspect the pluges. #3 plug where the boot of the pluge wire ends on the spark plug I can see carbon arking at the most 1/8 inch almost all the way around. Thinking the plug may be bad I replaced it. yet I still have the same problem and after running the engine the arking is back. running the engine with the cowling off (in a test tank) I hear the hi zapping. Could a slightly flooding cylinder (Vary rich due to float leavel) cause this to happen? I don't see the arking on any other plug.
