Re: Hopefully simple solution
There is a switch that quickly cuts the ignition when you shift so that the torque is let of the drive so it will shift easyer, (assuming that you have an outdrive) Its on the shifting mechanism ontop of the engine. Anyways this will sometimes wear out and stop working so that it wont restore the power fast enough so the engine will just die when its put into gear. Try replacing that switch, i had a friend with the same problem and this switch was the answer to his problems.