I have a 1981 115 Johnson outboard. It has run really well in the past with no problems. I tried to start it this weekend after it has sat for the past 2 yrs. It turns over very slowly and will not even begin to catch. When I pull the plugs and tried to turn it over, it turned at a much higher RPM. Yet when I replaced the plugs it slowed way down again. Almost like there is too much pressure somewhere. The starter really strugles to turn the flywheel with the plugs installed. Any ideas what I can do to get it started?