Treating bad fuel with Sea Foam [SOLVED]

I have repowered my 1986 42ft Regal with twin 454hp gas engines. The gas in my starboard tank is bad, roughly 2yrs old. I’ve tried to drain the tank and remove the old gas with poor results. I was told by a friend that I can add 16 oz of seafoam per 5 gal of old gas. Than run the engine at 1000 rpm’s until all the old gas was used up. My question is will burning 35 gals of treated gas gum up my 4 barrel Harley carburetor?

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Jim D.
Jim D.
1 year ago

Hi Scott – thanks for the question!!

Here’s what I’d do to get rid of the old fuel while keeping your new engines clean:

Supposing your fuel tank is larger than 35 gallons, top off your fuel tank with fresh fuel. One big problem with old fuel is it loses its volatility. The fresh fuel will give you enough volatility to burn through the tank. If you’d like to add Sea Foam at this point, you can, but I wouldn’t worry too much about finishing the tank. What’s next will be more important.

Once you’ve finished the tank of old fuel, add 5 gallons of fresh fuel and 2 full cans of Sea Foam High Mileage or Marine PRO. Then, run the engines until almost empty. This will allow the high concentration of Sea Foam to work quickly and effectively to clean any suspended gum/varnish. Then, refuel and operate as usual.

Adding Sea Foam to a low tank will work very well to clean any suspended gum/varnish that’s left from the old fuel, and will get your carburetor as clean as possible.

To answer your original question, burning treated fuel would not gum up the carburetor. However, using the high concentration method will be a much more efficient way to keep the carb clean after being exposed to the old fuel.