Yup I have also seen people do carb rebuilds on older motors, and not change old fuel lines, and fuel line gunk made it to the fresh carb from all of the handling.
well I changed all the fuel lines when I cleaned and rebuilt the carbs. It is running again now after putting new sparkplugs in although I do have yet to put it in the water to test it out
Also dont rule out a short somewhere. When the motor goes into a body of water, the ground improves exponentially. I have seen a shorted stator do odd things while IN the water. Just a possible scenario...... You could always check the battery voltage under load.
