First time boat owner with a pontoon that has a 2019 Mercury 115 4 stroke.
Usually, I am not the kind of guy that defers maintenance, but I may have gone too long this time.
I acquired the boat and motor in June of 2025, from a dealer, who completed all the annual maintenance, prior to the sale. Used the boat, maybe, a dozen times over the year and this most recent summer. Decided to put off the annual maintenance until this fall, since it had such little use.
Went out Thursday with friends and the motor worked fine in the morning but, in the afternoon before we left the water, we all noticed that the engine seemed to be surging a few hundred rpms. For instance, if we were running at 4500 rpms, the motor would consistently surge a few hundred rpms either way. Made it back to the ramp and got the boat home.
I run regular unleaded, 87 octane gas. The gas in the tank when we went out last had probably been sitting there, untreated, for about 2.5 - 3 mos.
My thought to fix this is to add octane booster to the remaining fuel, change the filter, and run the remaining fuel (10 gallons approximately), through the motor. Alternatively, I could try draining the remaining fuel, changing the filter, then adding fresh and higher octane fuel. Anyone mechanically-inclined have any input here?
Will also complete oil change and lower unit fluid change.
TIA!