Did Yamaha start re-cycling serial numbers?

[99yam40]

Sorry about that, I was thinking about and looked up a 25 for some strange reason.

If only one carb , both should be getting the same fuel mix, and no water entering cylinder, then I am at a loss as to what would foul just the lower cylinder plug.

Maybe condensed fuel/oil collecting on the bottom of intake or crankcase getting sucked into the lower cylinder.
I do not know

 

[bcripps]

Lower plug...

 

[99yam40]

Is that white specks with the black carbon or is it just light reflection?

How did you test spark?
Making sure it can jump a 1/2" gap would be good.

As you said you probably can not find a timing light, but if you could it would be a good way to look at how well the plugs were sparking while it was running.
I have read some of them can give RPM readings also from spark, so you could compare the top to bottom to make sure they both are sparking the same.

I would post some of this over on the other place to see if Rodbolt or Boscoe has any input

 

[99yam40]

With all that carbon on the plug I would look into cleaning up the inside of cylinder.

Yamahas ring free or combustion chamber cleaner would be good, but do not think you will find it.
heavy dose of Seafoam additive might be easier to find

How long does it take to get to looking that bad

 

[bcripps]

That's just light reflection. In real life it's oily and black. I'll try the half-inch gap to see if I can get the spark to jump it. I'll try it tonight after the sun goes down. It only takes a week or two for the plug to foul up like that. Someone accused me of running the engine too slow, which was probably true. But pushing it harder for the last month didn't improve performance. Just burned a lot of gas which I have to jerry-jug from the gas station; about a mile! Nothing's easy...

I did buy a quart of gas additive with a high percentage of PEA (?) Had it shipped in at great expense. I ran it through with about ten gallons of gas. Didn't do a thing.

You guys are very helpful and I really appreciate the time you're putting into my problem. Much thanks.
Bry

 

[clanton]

Stick your tongue to the tip of the sparkplug, if it taste of SALT, replace the head gasket.

 

[bcripps]

Yeck! Ok...

 

[bcripps]

Ok... did the tongue test. Didn't taste salty. Didn't taste good at all.
Seem to have good spark. Enough to give me a jolt, even holding the wire with rubber gripped pliers.
So thinking of that crusty head gasket. Could I be leaking salt water into the cylinder? Compression is good and the engine runs pretty well once warmed up;. It still starts on one pull.
Bry

 

[flyingscott]

I would suggest going into the carb maybe it's flooding a lttle bit and excess fuel will run down hill to the bottom cyl just a guess. Time for another taste test if the crust on the head gasket is salt that will need to be replaced. But be warned salt water motors love to break bolts.

 

[bcripps]

Thanks for the heads up re the bolts. Pretty hard to get anything fixed or replaced here in the DR.
I'm hoping that some of this crud will taste like potato chips! Let me give it a lick and I'll report back.
I want to order a gasket kit from the US before stripping down the carb. Need the motor for the daily trip ashore from the sailboat.
Thanks, flyingscott...
Bry

 

[bcripps]

Tasted the crud. Thought it tasted more alkaline than salty. Note that is evenly spread around the circumference of the gasket. Not concentrated in one spot.
I have never had the head off, so not sure of the configuration of the cooling water channels..