Soot in the exhaust.

Doc O Rock

Doc O Rock

Active Member
Mar 23, 2016
448
Belle Maer Harbor, North Channel Yacht Club
Boat Info
1999 380 Sundancer
Engines
twin 7.4 Merc
The other day, after a 4-hour run I stopped at the fuel dock and upon startup, I always check that I have good water flow. When I looked, I found soot in the water. The engine ran fine, but I did notice a sooty smell in the cockpit almost a burning coal smell. Any thoughts?
 
You might be having an issue with the choke sticking. It might be running rich.
 
Check your fuel pressure. Could be sticky injectors also. See if it will hold pressure after shutdown.
 
Doc trust me I'm definitely not a mechanic. I had this happen to me when I had my 220SD. It started out like what you are saying and got worse. I ended up taking it to a mechanic after it got where it would hardly run. They basically cleaned the fuel system and said do not run ethanol gas in the boat. Which I did before that because I was on a trailer. It was basically clogging everything up and made the boat run rich. Where do you fuel at? That is why I almost always go to Belfour's. I also put injector cleaner in every few fill ups. Maybe you could treat the gas with injector cleaner and hopefully it clears up. Beyond that is above my head...:D
 
I had a 99 340 that did this consistently the first two years I owned it. In my case it was unburnt fuel and I could never really smell an odor. A definite black sheen, not oil, on the water coming from both engines after restart. After several treatments of injector cleaner and aggressive cleaning of the flame arestors the problem went 100% away. Never any more black from the exhaust. I was quite pleased it wasn't something more serious (in my case).
 
Rich fuel mixture definitely causes soot at start up.
 
My normal fill ups are a Duffy's at Belle Maer but on my trip it was everywhere and I use the Star Brite fuel treatment at most fill ups.
http://www.starbrite.com/item/star-tron-gasoline-additive?category_id=569
I needed an oil change so I have asked my mechanic to check it out. I have to stop by Belfour's when I go by. As far as the flame arrestors, I changed to the K&N's last year.
What's your favorite injector cleaner?
 
I just heard from my mechanic, and he's baffled. He did see some soot on startup, checked the fuel pressure, and pulled all the plugs and said they all look beautiful. The plugs have about 50 hours on them, and he thought if one of the injectors was sticking, he would get a bad plug. Also the computer looked good. Hmmmmm. Thoughts? Also the oil didn't smell gassy.
 
Stee6043 said:
I had a 99 340 that did this consistently the first two years I owned it. In my case it was unburnt fuel and I could never really smell an odor. A definite black sheen, not oil, on the water coming from both engines after restart. After several treatments of injector cleaner and aggressive cleaning of the flame arestors the problem went 100% away. Never any more black from the exhaust. I was quite pleased it wasn't something more serious (in my case).
Click to expand...
What injector cleaner did you use?
 
If you were running rich the mechanic would have probably seen it on the plugs. Also, you mentioned an almost coal like smell in the cockpit. If you were running rich you would probably smell the pretty recognizable smell of unburnt gas.
 
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