HELP ! 2002 Mercury 115 4 stroke missing above idle

[theoldwizard1]

Okay,I am the classic weekend boater. I got the boat out for the first time this year and the engine is not running right.

Last fall, I drained all of the fuel and replaced it with fresh premium fuel treated with StaBil. I fogged the engine and buttoned it up. It started right up this spring on the muffs (EFI is great).

I get out on the lake yesterday and throttle up and the engine starts missing. Sometime it clears up, but above 4000 RPM it is almost continuous.

I checked the fuel filter/water separator. No water and filter looks clean.

The bulb will stay hard over night. In the AM 6-8 bulb pumps and the bulb is still not fully hard.

Of course all the marina in the area say they can get to it next week, so I am on my own for this week.

My guess is air leak on the vacuum side of the mechanical pump or mechanical pump diaphragm leak. Other guesses ?

[davidkuhlmann]

What do your plugs look like?

[Popeye]

What do your plugs look like?

Yeah, pull em.

[davidkuhlmann]

The spark plugs can tell the story of how an engine is running. He could have a fuel delivery problem but I'd also guess he could have plugs breaking down due to carbon.

[Popeye]

Perhaps so.