What should I do to clean a 1980 Sea Ray Sundancer 260 Mercruiser fuel system after sitting for four years? [SOLVED]

Thanks for the question, Mark!

Since the boat has been sitting for about 4 years, you’re on the right track by draining the old fuel first. Fuel gum and varnish is the #1 concern after sitting that long.

I’d recommend using Marine PRO. Here’s what I’d do:

• Drain the old fuel from the tank and carb.
• Add a small amount of fuel with a high concentration of Marine PRO (1–2 gallons of fuel and 1 can of Marine PRO). The higher concentration works much better and faster to clean fuel  gum and varnish than adding it to a full tank.
• Start the engine and let it run long enough to draw the treated fuel into the carburetor. If it runs, operate the boat for at least 20 minutes. Don’t be afraid to run it hard once it’s warmed up.
• After you’ve run the treated fuel through the system, refill the tank as normal.

That treatment will do a good job cleaning the fuel system.

Once you get it running well again, I’d recommend adding 1 ounce of Marine PRO per gallon of fuel to every tank. It’ll help keep the fuel system clean and prevent the fuel from degrading while the boat sits.