I have a 1990 90hp merc will not start. So I took one of the plugs out to see if I was getting spark and with it grounded to the block it fires. Then I put the plug back in and it will not start. So I took the plug out and it did the same thing.The motor is getting fuel and spark. This happened when I removed the center plug as well as the bottom plug. I only assume it would do it with the other one as well.When I say it fires I mean it will start and run with the plug out of the cylinder 3 inches from the plug hole. But put it back in and it will not hit a lick! Anyone.