Thanks for the question, Percy. Yes, absolutely. For an outboard motor, I’d recommend Sea Foam Marine PRO. It’s specifically formulated for gasoline marine engines and works very well to clean fuel gum and varnish from the fuel system.

For the best cleaning results, here’s what I’d do:

• Wait until the fuel tank is low (about 1/4 tank or less)
• Add a full can of Marine PRO
• Run the boat for at least 20 minutes before refueling

The higher concentration works much better and faster to clean fuel residues and varnish than adding the same amount to a full tank.

Once everything is running well, use 1 oz of Marine PRO per gallon of fuel to help keep the fuel system clean and stabilize the fuel between uses.

Thanks for the question!

If fuel gum and varnish is causing the hard starting, Marine PRO can definitely help clean it up. For the best results, though, I’d wait until the tank is low rather than adding it to the full 17 gallons. Then you can just use a single can of Marine PRO to create a high cleaning concentration. If you don’t want to wait until the tank is low though, adding three cans and then running it will help clean up any gum and varnish while it runs.

Here’s what I’d do with one can:

• Run the tank down to about 1/4 tank or less
• Add 1 can of Marine PRO
• Run the boat for at least 20 minutes before refueling

The high concentration works much better and faster to clean gum and varnish from the fuel system. If gum and varnish is what’s causing the hard starting, this will give Marine PRO the best opportunity to clean it up.

Hope that helps and let me know if you have any other questions!

Thanks for the question, Joe. Use Marine PRO (in the blue and white can) and add 1 oz per gallon of fuel, in every tank. It’s cheap insurance that’ll keep the entire fuel system clean and prevent gum and varnish from forming. If you can’t find Marine PRO, you can use Sea Foam Motor Treatment.

For an occasional cleaning, add a high concentration to a low amount of fuel. If you haven’t used Sea Foam before, that’s what I’d start with.

Here’s what I’d do: Wait until you have a low tank of fuel (1-2 gallons). Then, add a full can of Marine PRO to the fuel. Run your boat at least 20 minutes if you can (just don’t run out of gas!), and don’t be afraid to run it hard. After that, refill your fuel tank as normal.

Here’s a (rather lengthy) explanation of why a high concentration works best. For upper engine cleaning (fuel injectors/carburetor circuits & chamber deposits that can affect running performance), it works much better to add the full can to a low amount of fuel for two reasons, 1) the cleaning concentration is considerably greater and, 2) the cleaning effect will start much faster with greater effectiveness. If you were to add Marine PRO to a high volume of tank fuel, it might take several hours of engine running for a lower concentration of the treatment to work its way through the fuel lines and through the engine. Understanding the concentration approach will go a long way in terms of understanding how Sea Foam’s engine products work for overcoming fuel residue restrictions or a rough-running engine. Pay attention to starting, smooth idle, throttle response, hole shot, acceleration, and top speed. The #1 cause of each of these issues is heavier suspended fuel gum and petroleum varnish that restricts fuel passageways. The most important thing Marine PRO does is liquefy and clear away sticky gum and varnish restrictions so the engine can go back to starting fast and running strong.

Hope that helps and let me know if there’s anything else!

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.

Thanks for the question!

Yes, you can use Marine PRO and STA-BIL Storage together in the same tank. The two products are compatible and won’t interfere with each other.

That said, Marine PRO will protect the fuel from degrading and preserve ignition vapor on its own, while also cleaning and lubricating the fuel system.

For storage, I’d recommend adding at least 1 ounce of Marine PRO per gallon of fuel, then run the engine for about 10–15 minutes to make sure the treated fuel is drawn through the entire fuel system before storing the boat.