A functioning generator is, for reasons of safety alone, vital. The assembly delivers the magneto type ignition, renowned for the reliability that is so important to marine engines (and petrol aero engines for that matter, although planes have a double system for safety - they cannot float on air!).
The assembly is relatively simple with only four major parts, the rotor, stator, coil pulser and crank position sender. It would be highly unusual for all four of these components to fail unless the engine has been standing too long outside, and therefor they may be corroded beyond practical use.
More generator related parts you may wish to consider:
Add as many components as you wish to the same shopping cart, for example new washers 9299006600 and screws 9858005012 9798506210 9788006018 to replace those that are corroded or damaged beyond use, and still only pay the same fixed price shipping cost. Professional quality Gasket Seal:08C70K0234M. This component may have other applications within the Yamaha model range. Check the part-numbers you order are correct for your application.