CONTINUOUSWAVE

This is my first post and I am excited to become a new user of continouswave.

What would be causing my 2006 Mercury Optimax 75-HP DFI, three-cylinder, 1.5-liter, two-stroke engine to dump fuel out of the overflow port right into the ocean or on my driveway?

The engine is in great shape with only (roughly) 200-hours on it, and we take great care of it. Recently, we (my father) had trouble removing the "castle style" fuel filter. This was prior to purchasing the Mercury removal tool from Amazon, which I highly recommend. Basically the entire old filter was destroyed along with some of the aluminum threads on the Vapor Separator Cover. I am guessing that some of these plastic and aluminum particles have gotten stuck in one of the hoses, float kit, or somewhere else in the Vapor Separator Bowl. Most likely the float kit is jammed or broken and not shutting off the flow of fuel to the separator causing it to dump out the overflow.

So where do I go from here? I have removed the entire Vapor Separator Assembly and plan to take apart, clean well, and--hopefully--notice something obviously wrong. If not, does anyone have experience with this? Should I just replace the float kit regardless if it looks damaged/jammed or not? I also plan to replace the Vapor Separator Cover due to the damaged threads. Is this necessary even though the fuel filter can still screw in fairly easy? Should the gasket also be replaced after the cover is removed?

Any help/advice would be greatly appreciated.

Thanks,
Jared

PS: This engine is installed on my 1971 Boston Whaler Nauset, 16'7". Not that it matters.

I think your analysis is likely correct: the float mechanism that controls the high-pressure fuel pump must not be working, and the pump runs all the time, overfilling the fuel system.

Do you hear the pump running? I presume it is an electrically operated pump. I presume that the electrical pump is controlled by the float switch, and that the pump runs even if the engine is not started. If that is a good presumption, you should be able to turn the ignition key to ON, but not start the engine. Then you should hear the pump running, and continue to run until fuel spills out.

Do you have the factory service manual for this Mercury OptiMax engine? These engines have a complicated fuel system, and to perform work on them yourself your task will be greatly aided by having the service manual.

Update: 9/14/17

I have disassembled the entire Vapor Separator and did NOT find any significant debris or aluminum shavings. Basically nothing that is obviously the concern. Other than some minor corrosion and the Valve Kit Inlet seeming to have some carbonization on the tip, I can't pinpoint the concern. Pumps have been tested and running fine, so your presumption is correct jimh.


Is my best bet to replace the Valve Inlet Kit and pray that's the solution? Should I replace the entire Float Assembly Kit even though all the other parts are in good shape?

I also plan is to replace the vapor separator cover due to the damaged threads and also replace just the Valve inlet kit along with some of the rubber parts (gaskets/seals/o-rings/sleeve).



Am I doing the right thing here?

I don't have a factory service manual, I have been mostly following reliable youtube videos.

Any additional insight would be helpful. Thanks!
-Jared

UPDATE 10/23/17:

Repair worked. I still can be sure the exact culprit but I'm pretty positive it was the Valve Kit Inlet.

Glad to be back up and running.