Strange spark plug deposit

[noelm007]

I just changed the plugs during routine maintenance on my 90HP 4 strokes, the motors are running OK, but one plug had tiny green "dots" on the electrode, just about impossible to see except under very close inspection in bright sunlight, all other plugs were like new and no deposits, the green dots were quite hard and stuck to the electrode requiring a bit of digging to get them off. Anyone ever seen this, or know what it is? I have googled a few similar things, some say it's reverse "spark" on a waste spark system, not too sure I buy that one, other say it's anti freeze leaking into combustion chamber, definitely not that on an outboard, others say it's copper deposit from a failing valve coating, never heard of that, I really have no idea and have never seen it before.

[Greg Moore]

Copper was my first thought, no idea if any copper is used anywhere in a modern Suzy though. If you have a volt meter, carefully touch one of the knobs and see if it conducts to the main body maybe? You can also get cheap Chinese borescopes on ebay for like $9 that work on your USB port on a laptop or cell phone. Have had one for a few years, never know when it's nice to look inside something..

[noelm007]

It is a kind of Copper green, but I don't know if anything is copper coated as such, I might have a look inside just for kicks, but the motors run fine, and if I didn't look at that one plug in the sunlight I would never have known, all other plugs are like new (both motors) it just kind of puzzles me that it's there, might have been a bad plug? One thing that does kind of add something, my son had the boat out a few weeks ago and said the port motor sounded louder, I took it for a run and it sounded OK to me, and has so for the last couple of trips, I am just doing a routine service, plugs, oil and filter, fuel filters and impellor inspection (it was replaced last service, I only do them every second service) so no problems with either motor, just curious if there is an indication that "something" is going on.

[Hoosmatroos]

Do you troll a lot or run it hard?

[redlowrey]

It is a kind of Copper green, but I don't know if anything is copper coated as such, I might have a look inside just for kicks, but the motors run fine, and if I didn't look at that one plug in the sunlight I would never have known, all other plugs are like new (both motors) it just kind of puzzles me that it's there, might have been a bad plug? One thing that does kind of add something, my son had the boat out a few weeks ago and said the port motor sounded louder, I took it for a run and it sounded OK to me, and has so for the last couple of trips, I am just doing a routine service, plugs, oil and filter, fuel filters and impellor inspection (it was replaced last service, I only do them every second service) so no problems with either motor, just curious if there is an indication that "something" is going on.

Does the porcelain of the spark plug look any whiter than the rest, if the combustion chamber temperature is hotter than normal from running lean, it will deposit little brown spots on the porcelain of the plug.
These open loop engines run pretty close to stoich, eg air fuel ratio of 14.7 to 1 and if you had an injector not spraying properly could be running a bit lean on that cyl. Usually if you run hard you can get some redish to brown deposits on the plugs but you only have a problem with one plug. It probably wouldn't hurt to check the clearances on your valves.

[noelm007]

Boat trolls a bit during the summer, but runs pretty hard to and from the grounds (about 30-50 KLMs) white porcelain looks the same on all plugs, I will check valve clearance just to be sure, pretty easy job (kind of) I will see if I can get a photo good enough to be able to see the spots, I have one of those little camera gizmos, I might take the new plug out of the "odd" cylinder just to have a look and compare to another cylinder, might be a bit tricky getting down to the plug hole, but should be OK, at least it's a top plug, well second from the top anyway, so easy to get to.

[noelm007]

Just a bit of an update on this, most probably cause is a water leak into cylinder, need a leakdown test done, bit tricky on this motor with the plugs way down in a tube, but going to have a go and will let you know the result.