Black smoke on start of my Hunter 28 (2GM20G Yanmar engine)

[Davidasailor26]

In addition to Gary’s suggestions, keep a log of engine hours between refills. After a couple refills you’ll get a sense for how much fuel you burn per hour. With that you can always know how much fuel you’re down, generally to at least as much accuracy as a typical gauge.

 

[Tally Ho]

I have a 2GM20F and I burn about 1/2 gallon per hour of motoring @ 3,000 RPMs.

But check the top of your tank and look for some sort of visual gauge…like this:


It may not have a wire connected. This is a actually a mechanical fuel gage and there is a little visual gauge under that dirt.

But more importantly, I learned that this gage will drive an electric fuel gauge…which I installed at my helm.



But if you can’t find a gauge, put 5 gallons of diesel in the tank (or fill it) and start keeping track of how many hours you use the engine.

I made a little spreadsheet that I enter engine hours at the end of the outing, and it keeps track of how many hours. Or you can keep it in a paper log.

Greg

 

[Corinne 30]

Check your prop! This happened to me and I spent hours on engine-related checks and cleaning etc.. the issue was barnacles and growth on my prop. This causes the engine to overwork and create black smoke. Cleaned it by diving and scraping it all off. Immediately solved the black smoke problem.

ESPECIALLY if levels and temps etc. seem proper and you're still scratching your head - check the prop.

 

[jssailem]

I spent hours on engine-related checks and cleaning

You got to start someplace. Observe the symptoms. Choose the most rational place to start based on your boats history and your maintenance performance level. For some it is the engine. Others the boat hull and prop. Inspect first develop a plan then execute the plan. If the results are not satisfactory, move on to the next step.

Certainly the hull and prop can cause the engine to labor emitting black exhaust. There have been a number of boating reminders on both coasts regarding crab or lobster traps in the water. A wrapped crab pot line can be just as bad as a prop full of barnacles or mussels.

 

[Sinnerman]

Black smoke on startup:
Remove your injectors and take them to a shop for servicing.
They will test the spray pattern, firing pressure and if they seal (not leak / drip) after firing.

The injectors are designed to seal 100% after firing, trapping the fuel in the line between the injector pump and injector, so on the the next firing, there is no delay (lag).
If the injectors do not seal completely, after engine shutdown, the fuel under pressure in the injector lines will drain into the cylinders and will cause a nice black puff on startup.
Injector servicing (testing, cleaning, rebuilding) is a maintenance item, as well as periodically adjusting the valve clearances.

Temp spools up quickly after a few minutes after startup:
The thermostat is probably not opening.
Use a thermal heat gun (pistol) to check temperatures on the cooling path.
If it is not thermostat, and water is comnig out of the exhaust OK, then check the heat exchanger (clogged / needs cleaning)

Cheers

 

[odaydokay]

Have a careful look at that fuel tank the gauge may be built into the top of it.

 

[jtm]

you mentioned you were doing like 1500 rpm. Kinda slow. 2350 to 2800 (wave/wind conditions permitting) is more cruising normal. Otherwise some carb build up is likely in exhaust and cyl. At 1500 you won’t know if you don’t have the power you should have. I asssume your prop and hull are pretty clean.

Don’t know when/ if mixing elbow was ever replaced but if clogged/constricted by crud and rust at water injection point , you will not get much power. the black smoke exhaust is exhaust not being efficiently burned nor expelled from cyl causing incomplete burn. Replacing the mixing elbow ( and gasket). I had to replace the entire exhaust from back of engine up thru elbow bc the elbow was so rusted in place I rusted cracking the assembly to get it off. Its not a difficult r&r job. Lower aft Bolts removed, it lifts out over engine. Wear long sleeve flannel shirt as you reach around the back of engine to avoid forearm metal cuts

also your injectors, may be “weepy” allowing more fuel to drip into cyl.

 

[Deparlocean]

I bought my Hunter 28 5 years ago, and I took the injectors out and sent them for rebuild. Since then it starts on a quarter turn without any throttle up and does not smoke at start-up. I also took the aluminium tank out to have it checked and resealed because there was signs of small holes wanting to pierce through at the bottom corners and around, and I asked the shop to install a gage on it. The drawback to take it out, it is to cut an opening in the rear wall of the aft cabin. But I am happy that I will not have a fuel tank leak down in the boat.
As for the cooling system, I took out the heat exchanger to inspect and clean the tubes as necessary, along with a new impeller in the raw water pump. Everything done I never heard the "overheat" alarm, except when we took to lake Ontario two summer ago when the impeller failed (I had a spare one to replace it!) and never again since then.
To prevent black smoke and promote easy startings, I make a run full thottle for 5-10 minutes once in a while, rising internal temperature which burns up any accumulation in the cylinders. And my boat thanks me!