HELP - Mercury Motor Won’t Start - Carburetor is suspect

[Manerack12]

I’m trying to diagnose a no-start issue on an older outboard motor. The engine cranks/turns over and the flywheel spins. I have power, new fuel in the tank, and new oil. I replaced the spark plugs with new ones and installed them, but the engine still will not start.


Fuel line has an inline fuel filter. I removed the air box/carb cover and can see the carburetor intakes/butterfly plates. When I spray a little starting fluid/fuel into the carb throat, the engine pops/tries to start for about a second, then immediately dies. Without spraying anything into the carb, it just cranks and won’t fire up.


So far I have checked/done:

• New spark plugs installed
• Engine cranks/turns over
• Flywheel spins
• Fuel tank has new non ethanol gas
• Marina Grade 2 stroke Oil is present
• Inline fuel filter is present
• Air box removed so carb throats are visible
• Spraying into carb throat makes it briefly fire, then die

Symptoms:

• Won’t start on its own
• Briefly starts/pops only when fuel/starting fluid is sprayed into the carb
• Dies immediately after that
• Seems like spark/compression may be present since it fires briefly
• Suspecting fuel delivery/carb issue, clogged jets, bad primer/enricher, fuel pump, clogged filter, stuck float/needle, or fuel line/vent issue

My main question: based on the fact that it fires briefly when sprayed into the carb but won’t keep running, would you agree this is most likely a fuel/carburetor problem? What should I check next before removing and rebuilding the carbs? Should I first drain/flush the carb bowls, replace the inline fuel filter, check the primer bulb/fuel pump/tank vent, or go straight to pulling and cleaning the carbs?


Any advice on the correct diagnostic order would be appreciated.

 

[Manerack12]

Here are pics of the engine.

 

[jimmbo]

Welcome to iboats

How did you come to the Conclusion that this is Mercury?
It is an OMC Motor(Evinrude/Johnson)

What are the Compression Numbers?
Is the Spark strong enough to jump a 3/8" Gap?
Is there any Blockage in the Fuel System? Carb Circuits could be gummed up with Dirt, Gum, and Varnish. Inlet Valves in the Carbs could be stuck closed.
R&Ring the Carbs will also require performing what is called a Link & Sync.

Get a Genuine OMC Service Manual specific to your Model and Year of Engine. Stay away from 3rd Party Manuals


What Model is this Engine. A Serial # will certainly help
If it is a 2 Stroke, do not use Starting Fluid. While it can be used on a 2 Stroke Diesel, it can damage a Crank Case scavenged Gas Engine

I have no Idea what a Marina Grade 2 Stroke Oil is. I suggest using a TCW-3 Certified Oil. Myself, I prefer Motor Branded Oils.

 

[Chris1956]

Generally speaking, if she fires on ether sprayed into the carb throat, but not without, the fuel system, usually the carbs, have issues.

 

[jlh3rd]

you gonna need to pull the carbs most likely. You can try partial dis-assembly while mounted ...removing adjusting screws, bowls, etc. Lay a rag underneath to catch small parts and then using carb cleaner through all the passages....might get lucky.

Does the cowling have " insulation"...foam rubber type on the inside?
Is it "crumbly" ?
If so, strip it all out. That caused me a major headache until I figured out it was causing a problem being ingested into the carbs.

 

[Crosbyman]

how does one confuse Mercury with OMC products ?

 

[racerone]

The motor is black ??----Or a novice?----Perhaps the poster should post the procedure vused to try and start it.-----Pushing key in and holding it in when starting the motor?

 

[DeepCMark58A]

Use the same gas you mix for the tank put it in a spray bottle use that instead of starting fluid.

 

[racerone]

But this motor has the wonderful electric primer valve.-----Pushing the key in while cranking does the same thing as a spray bottle!-----It can not be made simpler.

 

[DeepCMark58A]

But this motor has the wonderful electric primer valve.-----Pushing the key in while cranking does the same thing as a spray bottle!-----It can not be made simpler.

If it is in working condition.

 

[racerone]

Those primers rarely fail.----Up to the owner to read the owners manual.----Learn how systems work.---Operating the red lever and squeezing the primer bulb is the same as using a spray bottle.------No wonder folks buy new motors with " turn the key " starting computer.