What could cause rough idle on '04 merc outboard 50 4 stroke efi?

Question

Just pulled the boat out of winter storage, I winterized prior to storing ie: change oil, change lower case lube and added Stab-il fuel stabilizer to tank. I pulled the boat out of storage and started it today and it seems to be idling rough. It was running fine last season. I'm thinking maybe the gas, not sure. Is there any test I could do to find out if it's the gas, maybe gummed up injectors or something.

Answer 1

I used to run Risilone through my fuel line until the engine would shut down before winter storage of my Outboards. I never had a problem but they all had carbs. I think you might have a durty injector from fuel residue. Even when you run them dry there is still gas coating the injectors. I would try some injector cleaner in the new fuel.

Answer 2

The problem sounds like it is fuel related.  If you had less than 3/4 tank of gas when it was put into storage, you may have some water in fuel from condensation.  Try putting an additive into the gas to absorb any water in the fuel  Run it for an hour or two at medium throttle settings then fill the tank with fresh fuel.

Answer 3

The product I use in my trucks and my boats is SeaFoam. At first blush this sounds like bad gas. Second, would be fuel filter, either on the engine or somewhere inline. The StaBil should rule out water in the gas.

Was the engine run out of gas last fall? Maybe that could gum an injector?

If you have blown the fogging oil out, maybe fresh plugs will help.

This one has me stumped. An '04 EFI with StaBil should be smooth as silk.