carbon exhaust

[m4boots]

For the last month every morning when I fire up the F75 Yamaha, there is a small, but noticeable, amount of carbon exhausted out of the prop. We have the boat on a local lake at 4600' of elevation. My question is, is this something to be concerned about, what do I need to check, and what needs to be done to correct this? The motor runs flawlessly otherwise.

[Sea Wolf]

Mark-

Just to be clear-

Was the motor doing this previously at the same lake/elevation?

What year is your Yamaha 75? Does it have fuel injection (and therefore computer controlled fuel ratio)?

Sounds like it's starting rich, then adjusting to the elevation after it starts/warms up. Perhaps an air pressure sensor is sticky/problematic.

We need one of the retired mechanics like Larry H, or one of the active dealers like Marc or Matt to tell us if this is within the normal operating sequences to be expected from that motor, but thought I'd ask a few clarification questions first.

Good Luck!

Joe.

[m4boots]

Hi Joe, thanks for responding and thought you might need more info, wasn't sure what to add.

1) The boat has been at this lake, except for a few weeks in Kootenay Lake, since I got it in May 2009. I believe it may have started this last September, with very little carbon coming out. Never noticed it at Kootenay which is about 1000' lower, but didn't look closely.

2)The motor is a fuel injected 2007, outdated but brand new when I bought the boat. Presently has 94hrs on it. Break in service and again last fall by myself since it runs fine otherwise.

[Matt Gurnsey]

I'm not sure what you mean by "carbon" coming out.

Is the boat in the water, are you running on the hose?

[m4boots]

Hi Matt, small (1" and less) globs come out the exhaust port in the prop and float to the surface at start up in the water. It's not fuel, grease, or oil, very thin and black and I'm guessing it's carbon. I'll try and take a picture this weekend.

[lloyds]

I have seen the same thing on most of the boats I have owned over the years, gas and diesel. Looks like you emptied your shaver in the water. I never worried about it.

[journey on]

While the posts on this forum are invaluable, I'd ask a dealer, also. If you know one who'll talk to you.

I used to see that on 2-strokes but not on the Honda. though I can't say I've really looked.

Joe gives a good explanation. The air fuel mixture has to be set for starting and then the feedback loop takes over. At altitude, that starting mixture must be rich.

Boris

[m4boots]

Thanks for the replies. I'll talk to Port Boat House and see what they think. I'll post anything if I find out.