Merc 40 2-Stroke Bogging Down/Losing Fuel Pressure

Discussion in 'Outboard Maintenance' started by Dillusion, Mar 9, 2015.

  1. Dillusion

    Dillusion devilray snob

    A Merc 40 that we just did a service on is now bogging down and losing fuel pressure at idle and WOT. Normally only after the engine is hot (not sure if related).

    The fuel primer bulb will go limp and if you hear the engine bogging down, you can pump the bulb by hand real quick and it will eventually gain pressure again and run fine. If you don't pump it- the engine will die out.

    Engine: 2001 Merc 40 2-Stroke
    Service that was done: Full carb clean/kit, fuel pump rebuild, new spark plugs, new inline fuel filter

    Possible causes: One tank of gas that was put in before this started happening, but after the service above, was from a sketchy gas station in the middle of nowhere, could be bad gas?

    Fuel water seperator was emptied when this started- and the gas was very cloudy. New fuel/water seperator was put in, but it's still doing this. Gas tank has since had 3 new tanks of fuel mixed in but was never pumped out.

    Possible solution due to the above: bad fuel maybe made it to the carbs and clogged the high speed jets? Maybe the fuel pump rebuild kit was bad from quicksilver when we did the service?

    Hole in fuel line somewhere? Clogged fuel line vent at the aluminum tank?
  2. DuckNut

    DuckNut Brandon, FL

    You forgot the push/snap on fuel line fittings. This is where mine did the same thing. Tiny leak in the seal and the system will lose suction.

    Mine would run for several minutes, lose prime and start to stall. As soon as I pumped it was good for a few more minutes. I changed the two fittings and all is good again.

  3. cutrunner

    cutrunner Cert. Yamaha technician

    Matty, this isn't aimed against you so don't take it personal.
    It's 90% something you did If it was running before you worked on it.
    I'm not questioning your abilities but with all the things you changed human error has alot of chances to be the problem. Maybe the inline filter is backwards, a jet not properly seated in the carb, a bowl not adjusted right, a diaphragm or spring upside down in the fuel pump etc.
    I realize you have come a long way since you first started posting on here, just saying we all make dumb mistakes sometimes
  4. Dillusion

    Dillusion devilray snob

    Well...One of the gaskets in the fuel pump was in the wrong order. ;D

    The square-shaped gasket and one of the diaphragm gaskets were flip flopped. Hopefully this was the issue. Have yet to test at WOT.
  5. cutrunner

    cutrunner Cert. Yamaha technician

    Glad to help my favorite Hella Bay snob lol ;)
  6. Dillusion

    Dillusion devilray snob

    devilray...just a devilray snob ;)