I have a 1991 Mariner Magnum 40 that stalls every time I put it in gear in the lake. On the ears in the driveway it runs good, idles good (though I am not sure what RPM i am running at) and shifts in and out of gear without issue. As soon as I take it to the lake and try to shift into gear it stalls. Pushes water until the motor runs out of inertia (about 5 seconds). Any thoughts what may be causing it to stall under load?
