Is it OK to put more Marine PRO in a 4 gallon tank? [SOLVED]

Thanks for the question, David!

Yes, you can absolutely put Marine PRO in 4 gallons of fuel. Add the whole 20oz can and run it until almost empty before refueling. That concentration will do a great job cleaning up the fuel system (for cleaning, it works better to use a high concentration like that…)

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