The CD’s are fairly low compression trolling motors and will smoke on a cold start, just like any two stroke motor will. Excessive smoking while trolling could be caused by too low compression (worn rings), the powerhead running too cold, as in icy water, or the carb being set too rich. These are the most common reasons if the fuel mix is correct. A plugged puddle drain will also contribute to oil fouling of the plugs.
Some owners used to pull in the gear and run the motor at full throttle for a bit to help clear out any excess oil in the motor and burn any carbon buildup off the plugs. Going to a slightly hotter plug can also help prevent fouling if the motor is ran at low speeds for extended times. You don’t mention what year the motor is so I assume it has no thermostat and requires a 16:1 mix. If it is thermostat equipped, it must be installed and working properly or the plugs will foul.
EDIT: Just noticed, it’s a ’56 but not sure if it’s an Evindure or CD.
