86 Mercury 50hp 2 stroke will not run!

[racin4ds]

Hi guys, I apologize if this really isn't the place for this but I'm reaching out in desperation here... I'm a very savy, certified mechanic and usually find my way around just about anything that runs but I have a good friend of mine's Mercury boat engine at the shop and it is causing me to lose what little hair I have left!!

Its an older unit but not many hours on it. 3 cylinder 2 stroke. All 3 spark plugs replaced, carbs pulled apart and gone through, float heights set, all jets are clean and clear etc. I have verified spark with a spark tester on all 3 holes and also checked compression-

110-100-110 respectively.

This thing will not attempt to start! Every now and then I'll get a pop in the exhaust but thats rare. I have even went as far as to give it a burp of ether straight into the carb and nothing! I've pulled the flywheel and reinstalled, checked TDC etc.

I'll admit, I'm not a boat mechanic, never seen one before now but its an engine, and a 2 stroke at that. They have always been the most simplistic things ever to work on and figure out!

 

[ragtoplvr]

If you have compression, fuel and spark at the right time it will run.

Is the gas fresh and not full of water. Is the crankcase not flooded with oil oil or lots of gas.

A spoonfull of oil in each cylinder will help the compression.

Broken reeds prevent getting fuel. Are the plugs wet with fuel. Does it suck air in the carbs, and not spit back.

Spark timing, could the coil wiring be messed up. A timing light will tell.

Rod

 

[Donald]

My guess is that its an ignition problem. Have you tried to look at the spark for each cylinder?

The Mercury 2 cycle engines were one of the first engines to get electronic ignition. My 1987 Merc (4 cycle) I/O has electronic ignition and so I will guess the two cycle has it.

From what I remember there was not a lot of trouble shooting info in the Merc service manuals. Many had "swap in working part" as the method to determine if a part is good rather than take measurements.

Ask on the BOATERED.COM forum.

You do not want to be forced to buy new Merc parts.

 

[racin4ds]

Thanks Guys, That has always proven true on anything I've worked on and is what has me so baffled here. We have spark, fuel and compression!

I'm honestly not certain the timing is right. I'm looking into that as we speak. I've set it to what I assume is TDC by putting cylinder #1 at TDC and aligning the pointer to the "0" on the flywheel.

I haven't been into this engine far enough to know if it as reeds or not. But yes fuel is good, plugs are new and spark has been checked on each coil.

Interesting enough your comment about the carbs sucking in air and not spitting back has me thinking, I do not seem to have any vacuum at the carbs, I went to hand choke the engine the other day and did not get my palm sucked in like you normally would!

 

[andyd]

Total wild guess. One of the crankase seals is sucking air.

 

[Kamele0N]

Does this engine have reeds? If yes...I would check them...maybe they are stuck...cracked...with specks of rust...

2nd after that I would check crank seals (wich was mentioned above..)

 

[JTK]

What's the history of the unit? Was it running fine and just quit, or was running before it sat in storage?

 

[Kawiguy454]

+1 crank / case seals. I had a 2 stroke motorcycle that had a bad crank seal. Net effect is that it loses vacuum to pull in air/fuel. When piston travels up a vacuum on the case is created that pulls the air'fuel charge into the case. When the piston begins down again the case pressurizes and forces the fuel charge up into the combustion chamber. Leaking can also occur between 2 cylinders. A motor that old probably has old dry cracking seals. Even if you got it to run it wouldn't run well and you could burn a piston if a cylinder leans out.

 

[Silk]

Outboards usually don't have exhausts blocking with carbon, but worth a look if you are running out of ideas. Mercury of certain periods were prone to corrosion at the bottom of the powerhead, this could damage the lower seal and crankcase. I don't like the crude mechanical advance off the throttle linkage those old outboards had, so make sure that's all working as it should.

We had an outboard a few years ago that ran, but 4 stroked all the time. We threw everything at it. Last straw was plucked...and we found someone had secured cables and wiring to the remote, and put a screw through a couple of wires. Took a long time to that simple fix.

 

[dwendt44]

Yes on reeds. Wouldn't hurt to pull the exhaust cover and take a look.
Reeds could be stuck or bent-unlikely but who knows.

My 2¢

 

[racin4ds]

Thanks guys, will chase the reeds this weekend when I have more time. Thanks for all the good suggestions and insight!

I don't know the history on this thing at all, my good friend bought it not running and brought it to me.

 

[BrocLuno]

To check timing, use timing light. Make your own marks. Put cylinder 1 at top dead center and make some sharpie marks you can see. Spin it and see what your timing light shows? 10* BTDC should get you going...

See if it will suck your hand onto the carbs when you spin it over? Or make a quick plate and use a vacuum gauge. If it won't suck your hand hard, it has reed/seal issues.

If the timing checks OK, pull the plugs and put some 2-stroke mix in each cylinder. Spin it. It should sputter and fire for a few revs. If it does, it's not compression or ignition ... Then it's reeds and seals ...

Those old Mercs were really stout engines. It may be worth fixing as they run well and long, when they get running