Runs rough under load and boat vibrates increasingly with more RPMs

[rgfoote]

[h=2]Your engine:[/h] 2003 Mercury Outboard 60EFI [ELPT/BF 4] serial # OT767978 Low hrs.
runs rough under load and boat vibrates increasingly with more RPMs Goes about half speed per RPS as normal, smooth running.. Runs great with muffs at idle and WOT.. Primer bulb will not get firm. Replaced pick up tube, fuel line and in line filter. removed engine fuel filter for inspection and replaced. A few specks on bottom of bowel, but filter clean. Was told fuel pump needs rebuild. Could it be dirty past the engine filter? Maybe the parts are old from age?
Where online to find a rebuild kit?
Where to read about fuel system trouble shooting? (on MY engine group only)
Thank for your time

 

[jimmbo]

You say it runs smooth in neutral, but in shakes in gear. What condition is the prop in? I hope you are not revving past 2000 in neutral

2 or 4 stroke?@
Is it firing on all cylinders?
Is the primer bulb new?

 

[Texasmark]

I was going to say prop (or bent prop shaft) too but not after you said WOT runs fine. I don't know the mechanism on an EFI engine on priming. On a carburetored engine, the needle valve in the carb is sealed off by the action of the float when the bowl is full. When this seals off the bulb should pump up to hard. If you had a leaking fuel line, crack normally, especially with the year of your engine then it would let fuel out and bulb would not firm up....but you should be able to find fuel where it doesn't belong in the engine. Other place would be the fuel pump diaphragm or internal check valve leaking fuel back into the combustion chamber where you wouldn't see it like a cracked hose.

Fuel injection requires an injector. Injector requires some kind of pressurizing device since the injector has to overcome the pressure in the combustion chamber when it squirts fuel. That means a pump. Could be that you have 2 pumps, or maybe the one does all the work. Whatever, go down the fuel line as far as you can and pinch it off. See if the bulb gets hard. If not back track to the bulb and if no takers, suspect your bulb which you didn't say specifically you changed (when you got a new fuel line).

Those little specs, were they black? If so that's fuel line deterioration and I blame that on ethanol fuels as I never had that problem over the years before using such. On my last engine the line started doing that at 10 years of age.....2002 90 triple looper.