2004 Mecury 90 hp wont start


Oct 11, 2021
I bought a pontoon boat with a 90 hp Mecury, 2004 outboard. The guy I bought it from said it had been sitting for five years but was in good shape when he put it up. I flushed out the fuel tank and line to the bubble. Put new spark plugs, new battery and fresh gasoline. It turns over but will not start. So I got some starter fluid and sprayed some in the intake. It started and ran untill it used up the starting fluid. Does anybody know if these motors have a shut off valve on the gasline somewhere that I cannot see it? Or can somebody give me an idea what to do next to get it running.


Jan 22, 2002
since you've been waiting, i'd say - did you research the forums for that motor? i don't know about a shut off valve. but if you have plenty of time, you can run a piece of fuel line from a tmp container of fuel/gas into the carb connection. or keep slowly pouring a trickle in carb. if it keeps running, that should let you know the engine will work - then concentrate on the carb. if tmp connected (by gravity - jug held above the carb level with a tmp fuel line) and its running ok - then look for trouble in the carb fuel line- to tank. probably sounds too elementary for good. but its really down to that. but perhaps still - a shutoff somewhere. sorry can't help with that. i've had weak suction on old motors - mechanical diaghrams. had to make new gaskets out of cork & the felt paper kind (its seems like felt paper/ roofing tar paper)


Supreme Mariner
Oct 30, 2002
Follow this starting procedure.

Open fuel tank vent

Check the kill switch, place in "run" position

Squeeze fuel primer bulb till firm.

Advance the throttle 3/4 way or more, without putting it in gear. -- This is done by either pushing a button in the center of the controls, or pulling the shift handle toward the driver, or raising the fast idle lever, all depending on what control unit you have.

Turn the key to the on/run position.

Activate the choke (fuel enrichment valve) by pushing in on the key. The valve is only open while the key is being pushed in.

Turn the key to start while continuing to hold the key in.

Release the key and choke when it starts.

3-5 seconds of "choke", is usually enough.

Be ready to pull the throttle back toward the idle/neutral position, when the engine starts and the revs increase.

Continue to pull the throttle back as the engine warms up.

You should not have to use the choke much, if at all, once the engine has warmed up.

Engine should start within 10 seconds of turning the key.


Supreme Mariner
Dec 20, 2005
In Roscoe's solution, the "kill switch" is an ignition killing switch at the operator's station that is made for a lanyard attached to your person while operating the boat....if you have the lanyard attached and fall overboard, the boat stops. If his starting procedure doesn't work:

You said the engine responds to fuel stimulation. Therefore you are chasing a fuel starvation problem not an ignition induced problem. If engine was stored with fuel in it....the PO turned the engine off with the key and put it in storage type thing....no attempt to consume all the fuel contained within the engine, then you probably need to pull your carbs and clean them out and install new carb kits. While you are at it, you might as well include a new engine mounted fuel filter ( I like to cut the old ones open and investigate contents), and fuel pump kit as the diaphragm gets stiff over time.

Your comment "replaced line to the bubble..."? Are you referring to the bubble as the squeeze bulb in the inlet fuel line? They get stiff too and internal check valves can cease to seal properly meaning that needs replacing too.

With all that said, with long term storage, you really need to replace the impeller in your water pump also, located in the top of the lower unit...the bottom end section of the engine where the prop gear box is located. A service manual would be real handy.

Follow the above suggestions and when finished, post back as to what happened and any comments.