15 MSH missing in lower cycilinder

[zenoahphobic]

I can only suggest that exhaust sludge is getting pulsed back into the bottom cylinder. This could be due to some alteration in the port and exhaust chambers through breakage, cracks or corrosion.
No other answer as engine does not have additional oiling to the bearings. If it did then the bottom cylinder would be getting to much oil this way.
Gravity has a way of always punishing lower cylinders when something is amiss.
Unless an expert tells you otherwise I would be examining behind the jackets and critically at the bore and exhaust ports.

[rodbolt17]

and folks, that is what burning fresh/brackish/mineral laden water looks like on a spark plug.
easy peasy if you know how to read a plug and its parts.
parts being side electrode,center electrode and the rest that doesn't do anything other than help seal a hole.

next time I get one burning saltwater I will try to get a good pic of what that looks like.

[robert graham]

and folks, that is what burning fresh/brackish/mineral laden water looks like on a spark plug.
easy peasy if you know how to read a plug and its parts.
parts being side electrode,center electrode and the rest that doesn't do anything other than help seal a hole.

next time I get one burning saltwater I will try to get a good pic of what that looks like.

Can under certain conditions water being burned in the cylinders cause it to flash to steam, actually scouring the plug and combustion chamber yielding a very carbon-free, clean surfaces?....I remember years ago pouring water through the carb of a running engine to remove carbon. In fact, I had a chunk of carbon break loose on my 350 Chevy and rattling around in the combustion chamber sounded exactly like a rod knocking....in fact, I headed for the Chevy dealer right away and by the time I got there the carbon had broken up and was gone!...no big problem!...

[zenoahphobic]

Can under certain conditions water being burned in the cylinders cause it to flash to steam, actually scouring the plug and combustion chamber yielding a very carbon-free, clean surfaces?....I remember years ago pouring water through the carb of a running engine to remove carbon. In fact, I had a chunk of carbon break loose on my 350 Chevy and rattling around in the combustion chamber sounded exactly like a rod knocking....in fact, I headed for the Chevy dealer right away and by the time I got there the carbon had broken up and was gone!...no big problem!...

I would agree water ingress usually cleans the plug and chamber, just as steaming cleaning is effective elsewhere.
Mineral build up like suggested would require a lot of water to get that much deposit. Unless the OP is running his boat in bore water.
Rodbolt please explain as you suggested it is not salt water.
By what means is the water getting in?

[99yam40]

I am sure it put some dents in head and piston before that carbon headed out the exhaust.
Of course the head was cast iron but piston is aluminum and dents easy.

As for as the OP problems goes, I was thinking once motor warmed up and grew some due to heat the leak may slow down or stop.

Or when up to running temp the small amount of water entering cylinder was flashed to steam and not shorting out the plug so it fired the cylinder better.

Only thing that suprized me was he said somewhere that there was not any white mineral specks on the plug what the pic showed was light reflection
So I would like to see the pic from Rodbolt of another one burning water also.

Always good to learn.


To OP, sounds like pulling the head is needed and inspecting exhaust plates and other parts for cracks, corroded holes, or gasket problems

[rodbolt17]

you guys and the steam cleaning theory are totally funny.
wrong as heck but still funny.
makes me think of unicorns and myths.

[zenoahphobic]

you guys and the steam cleaning theory are totally funny.
wrong as heck but still funny.
makes me think of unicorns and myths.

Right as heck, maybe your missing something in your water.
Water in a cylinder in a running engine invariably cleans out the dark oily deposits on the plug, cylinder, valves and piston tops. Some crust may well remain.
I would have thought you commenced your training back when engines were in the steam age and you would have seen many engines where water has leaked into the combustion chamber. One of the clues when the faulty cylinder appears much cleaner and of distinct different colour than the others with expected deposits.

[TownsendsFJR1300]

And, as someone posted, even thou its a TWO STROKE (visible in the first picture), if running properly, WILL have a spark plug burning as clean as a four stroke.

Maybe a little darker with pre-mix, idled a bunch....

Certainly NOT what the Op's plug looks like...

[99yam40]

I was leaning toward water in combustion chamber, but I have never seen one that caused a plug to look like that before. And he said it only takes about 2 weeks for it to look that bad from a new plug.

There is not much that I can think of that can cause a 2 cylinder single carb 2 stroke premix motor to foul just one plug like that.
This is why I ask the OP to post here to get info from Rod and Boscoe or others that have seen this on a plug.
Rod has said he has seen it due to water, I trust what Rod posts

something I have seen was water will stop a plug from sparking properly if enough gets to the plug. this is probably why he says it misses bad at start up
That is what happened to the only motor I personally worked on that had water getting into a cylinder.
I do not remember what the piston looked like, but the plug did not look like his plug, and it had water on it when I pulled it.
It would fire right up and run well once I cleaned the plug off and put it back in. But once you turned it off it would not hit on that plug until you pulled it and cleaned it off again

It got me home at least that day.
I pulled it apart the next day , surfaced the head by hand on a piece of thick Plexiglas with some wet sand paper with running water across it and put a new gasket in it . Ran great after that.

[bajakeith]

lower plug issue

I would do a high speed shut down and look at the plug...most plugs that ingest water will be VERY clean..as in like steamed clean..also since it's the lower piston he might want to ck the lwr crank seal...........Sir Rod bolt,, I just reread this thread and don't understand your thought's as I have seen many,many motors over the years with water ingested and a VERY clean plug and piston crown... a Honda cicvic CvCC motor comes to mind as in many of them..pull plugs and any cleaned.. time to pull Da head...

[zenoahphobic]

Looking again at the spark plug picture, the plug would have caused considerable trouble before it got to this state. Interesting that centre electrode doesn't have much on its top but the insulator is covered.
Yammie15 is that stuff soft? Because it looks a bit like the residue from cooking say a BBQ.
As this has become acedemic , is there a service that can identify the components of this deposit? Would it tell us anything anyway? Thinking what minerals such as calcium and iron or whatever that would be present in water but not in fuel or oil?
Yammie15 do you run this in dirty freshwater? Please post your results.

[99yam40]

hard to believe there are so many that post stuff without reading what the OP posts

[yammie15]

The Bay is a commercial harbor so the water is real dirty. There is tidal flow and fresh water fed from a couple of streams. I would call the water salty more than brackish. Fish live here but I sure as heck wouldn't eat one!

The crud is oily-soft and easily wipes off.

If I pull off the head, will I have to have the surfaces machined? I'm in a real backwater here with few services. No one I would trust with my outboard. Like I said, it's my only source of transportation so repairs would have to be done quickly to get the engine back in service.

Wish I still had the Yammie I bought back in '93. That was a gem.

Thanks all... the information is somewhat overwhelming but really great.
Bry

[99yam40]

No way of knowing how long it will take to fix it until you find out what is wrong with it and how well it comes apart.
Might need to sail to a place that has the stuff needed to have it fixed or pick up another motor before ripping this one apart to have it fixed.

They had boats that got back and forth to sailing ships long before the outboard motor was invented.
maybe you will just need to moor closer to shore while you work on it

[robert graham]

Buy your required new gaskets before removing head....if your head is warped you can lap it back straight with a few sheets of Emory cloth type sandpaper laid on a solid/flat surface, then slide head across in a figure 8 pattern until flat....A shop manual would be very helpful with details for this job...Also hope the threads on head bolts are not corroded in place causing them to break off upon removal(especially with saltwater motors)....then there is a tightening sequence with torque values for head bolts....good luck and keep us posted with your progress...