I can tell you my experience with a Yamaha 90 that I owned for ten years. I put in plugs and an impeller every other year. The motor
never saw a shop or a mechanic. Itoo used the recommended Yamaha additive. After the fresh water flush I would disconnect the fuel line at the motor and let it run down. It would lean out toward the end and start to race, so I would then throttle back. I never manually drained the three carbs. Great motor, sure wish I still had it.
