I have a 115 Merc 4-stroke, always done it myself, no problems. I run seafoam in the gasoline and spray the cylinders down with a fogging oil when I put it up. 2002, 7 years and still running great!@
Change oil/filter and lower unit oil.Fill the gas tank,add Stabil or SeaFoam. With engine running(hose attachment on motor) a few minutes, fog it about 15 seconds at the air intake and shut it off.Drain water from the that water flush hose on the side of motor(Yamaha).
I Seafoam the gas. Make sure its running through the motor then disconnect gas line and run it out. I fog the intake (disconnect spark and turn over engine) but usually not the plug holes because its difficult getting plugs out. Normally I would hit them too. Drain and refill lower unit. Good to go. That is what I have always done and will continue to do so. I empty remaining boat gas from can into my truck. With internal tank I would just leave for next season since it is treated. Some people top them off before storage but I have always topped it off with fresh just before I run it the next spring.
Winterizing a 4 stroke
