How much Sea Foam should I add in a 1989 Johnson 2 stroke running 50:1 premix? [SOLVED]

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!