Black smoke

[seaplane]

Hello, I have a Pearson 27 , Universal M-12 diesel engine and when i put more throttle than a cruise normal gas, it spend a black smoke, can somebody tell me what happen...

thanks.

Alan
Pearson 27 Hull # 40

 

[bobtigar]

Check the simple things 1st. Are you burning road diesel-it has a lower cetane rating than off-road diesel. k the air filter. If its clogged, clean the screen or repl the filter. Bob

 

[Honeyman]

Check to see if your prop is fouled with growth, hows clean or not is your bottom. Are you able to run engine up to wide open throttle? Could very well be exhaust elbow clogging.

 

[capejt]

I discovered he same problem this weekend. It only gets to full throttle without a load on it. Since I don't have a tachomoeter, I can only relate in boat speed; where I usually get 5 - 6 knots at full throttle (with no smoke) I can now only get to about 4 knots before I get black smoke. And even putting up witht he black smoke, I can only get about 4.6 knots out of it.
I tend to agree that that the bottom and/or prop are dirty. I pulled my speedo paddlewheel and it was encrusted with barnacles.
Isn't a dirty fuel filter also a cause? I ask because I'm not too confident with the fuel I've been running on this season, it's about two or three years old.

 

[jimg]

Black smoke is unburned fuel. The full throttle position is pumping the maximum amount of fuel to the engine, but you are not getting enough rpms to combust that fuel. The fact that it will rev with no load confirms it. The importance of a clean bottom can't be overstressed, it makes a huge difference in the overall performance and enjoyment of the boat. There is a reason that serious racers have their bottoms cleaned at least once or twice a month around here, and will have a pre-race cleaning the afternoon before or even the day of a race. Spend a little money. There must be a dive service in your area that can clean it for you. Your sailing and motoring will both be much improved.

 

[Mike Holibar]

I'm with Jimg on this one. She needs a clean. On the otherhand if your boat has always behaved this way then it is possible you are "overpropped" a term which means your propeller will not allow the engine to develop full revs and therefore full power. In that situation then engine max revs WOT are less than rated max rpm resulting in black smoke, less power, and excessive fuel consumption. Most modern engine manufacturers state that this situation would void the warranty. The solution is to match the propeller correctly to the engine so that it can develop full rpm at wot. No more black smoke, more power and lower fuel consumption will be the result.

 

[zeehag]

how often do you actually USE your boat??? do you place her under load often or rarely to occasionally?? how old is the mixing elbow for exhaust---many places to go ----if no0t used much, will soot. if elbow is clogging --will soot. if injectors dirty from bad or dirty fuel--will soot.....
if air cleaner is clogging -- will soot and produce low power to water.......goood luck.

 

[capejt]

Don't know about Seaplane but for my situation, whenever I use the engine it's at fulll (or nearly full) throttle. Use is about an our each week. The air cleaner is new, the elbow about is about eight years old. A question about the elbow though, If it were clogged wouldn't the flow of water through the exhaust be slowed as well? It seems to be just as good as ever.

 

[zeehag]

with my exhaust mix elbow, there was flow just like normal and there was black smoke and there was minimal performance. with a friends there was normal water outflow and black smoke. he cleaned his--i replaced mine---same amount of outflow but more performance. he has a 3 gm(D) i have a 2 QM 20H......

 

[capejt]

I just came back from a closer inspection. What I found was that all fuel line connections were fine, so air in the system. The elbow's exterior "coating" was flaking off (in rather large chunks). I ran the engine at the dock. Wihtout any load she revs up to max throttle no problem, no smoke. Put in gear (tied to dock) and slowly bring it up to max and get smoke near the top of that curve, heavy black smoke at full throttle.
I think in view of the exterior flaking and the smoke, it would best to replace the elbow.
Of course the prop could also be at fault here. I'm trying to find a diver to clean it, and try again.

 

[NYSail]

Check your bottom and prop. 2 seasons ago about this very same time my yanmar did the same thing. I dove and found the prop to be a large knot of barnicles and the bottom had a little fuzz. After it was cleaned off the boat ran great with no black smoke....

If this fails to correct the problem, the exhaust elbow would be my next choice...