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Y25 Mk2

May 10, 2014
Yamaha 25mk2 Victoria
What a fun boat! Im two years in, and loving it. Everything except the engine. Looking for advice. It starts and idles well, but as soon as its underway spits out black smoke and sooty water. I had it looked at 2 years ago - they checked fuel injector etc but said all was ok. Now, it seems to be putting out less hp. We motor very, very slowly and yesterday into the marina heading into the wind with little current were being pushed backward! Any suggestions? It has been hauled out in 3 years so maybe time to look at the bottom/prop? I'll probably have the engine looked at again as well. Happy for suggestions.

Some have suggested I just mount an outboard. Would kinda suck to just leave that diesel sitting there. If i were to do this, does the transom need to be reinforced to handle a 10hp outboard?

May 1, 2011
Pearson 37 Lusby MD
First guess is a clogged mixing elbow. Happened to me a couple of years ago. Folks on this site were quite helpful in troubleshooting.
May 6, 2012
Hunter 28.5 Jordan, ON
I don't know which engine you have, but the absolute last option that I would even consider, on a boat with a running (albeit poorly) diesel, would be mounting an outboard.

Diesels are simple. Find a competent diesel mechanic who can properly diagnose the issue. ' Checking the injectors' and leaving it at that doesn't qualify as competent.
Jan 4, 2006
Hunter 310 West Vancouver, B.C.
Some have suggested I just mount an outboard. Would kinda suck to just leave that diesel sitting there.
I think you need a new crowd to hang with.

Diesels are such rugged little buggers that you should be able to get it back to REASONABLE running condiiton with a minimum of $output$. Certainly much less that an outboard.

As Kappykaplan says, a likely problem is the mixing elbow. Check the archives here for info. Follow that with fuel filters and air filter. These are all things you can do yourself.

One final suggestion, watch the dock rats. Yours checked the injectors and said all was well :doh:. Do some research if you want to find a competent mechanic. OR if you're handy with tools, a SELOC manual is about $30.00 and the Yanmar shop manual is about $90.00. Certainly cheaper than a mechanic for an initial look at what the problem might be.
Feb 26, 2004
Catalina 34 224 Maple Bay, BC, Canada
Learn to work on your engine. Read this forum. Do "searches" on your subject. ALL of them have come up, over and over again. Find a website about your engine, I'd bet there is one, if not many. Exhaust elbows are a recurring, constantly recurring, subject for your engine. Learn what it is, where it is, and how to either fix or replace it.

Get the right tools.

Get your bottom at least cleaned, if not get it hauled, you're probably dragging around 3 years of crap on the bottom and the prop. This is basic stuff, you really should know by now. Do a search on bottom cleaning - there's a really good diver here named fastbottoms who posts regularly - read his material.

Look, none of us was "born" to be a diesel mechanic. We can all PROVE that by saying that few of us have ever found a good one! :) DIY and it will get done right. All it takes is a book or two, or doing a lot of reading on the internet and forums.

It's simply a safety issue, especially where you sail.

Good luck, happy learning.

PS - We know what boat you have, but I have no idea what engine you have. when you ask a question, it's important to help us to help you to tell us the details that matter. Thanks.
May 10, 2014
Yamaha 25mk2 Victoria
Thx for the replies. I have the yanmar ysm-8. Should have posted this! I've been learning lots - redid ignition, wiring and batteries last year as well as some deck work. I changed the fuel filter last year but still sorting out the exhaust elbow thing. I was just wondering if anyone had other suggestions. Engines are new to me so it's been a bit of a learning curve. On the hunt for a reputable mechanic to help.


Aug 30, 2010
yahama 25 Hong Kong
Isolate the problem , whether it is due to a foul bottom or foul propler or the engine itself . You said it was hauled out 3 years ago, so it is time to check .

I have the same boat and same YSM8 for some 30 years , it is a pretty reliable engine if properly maintained.

Disengage the gear , run the engine at different rmp to check any black smoke and the water colour .If black smoke comes out when the gear is engaged , it mean the engine is overloaded ......... by the foul propller or the combusion problem due to the injection nozzle or the cylinder pressure .

Isloate the problem step by step , and get the right one to fix the problem . No point to pay a mechanic to clean the bottom and the pro.

Good luck .
May 10, 2014
Yamaha 25mk2 Victoria
Much better!

Turns out the prop was encased with barnicles. All cleaned off and motors wonderfully now! Still working on routine engine maintenance.