engine vertical or horizontal. I think the YSE is the horizontal. The only real differences are irrelevant to your problem. A trick not commonly known anymore is to torque the top bolts on the horizontal heads about 10 foot/pounds tighter than the lowers. Ours dates to about 1976 to 1980. Your YSB is about the same age. I've had the crank in my hands so I know this engine pretty well.

There is a significantly different gearing between forward and reverse. We have to remember that.

So, why diesel in the exhaust.

Are you running her hard? She is designed to run at about 75% of maximum engine revs. Running her slow might case unburned fuel.

How big a prop are you swinging? Too big a prop will result in unburned fuel.

Perhaps a leaky intake valve?

Is the timing correct?

There is a swirling precombustion chamber (small cup) to divide and spray the fuel at the end of the injector in the head. Is it clean and the holes unobstructed?

We have never changed an injector and we have put about 4,000 hours on the engine, much of it charging batteries, in th last 18 years. I really think they are pretty indestructible. But a check is cheap - so why not? Still, a bad injector injects too little fuel, not too much. I'll be surprised if it is an injector.

You can get a good manual cheap. And the engine you have is about as simple as a diesel can get. A set of metric sockets, combination wrenches and a cheap torque wrench will get you through.

Pull the head and little valve combo. A head gasket and exhaust gasket are the biggest requirements. They aren't expensive.

Check these sites: http://www.yanmar.com.au/qrg/yse-12.pdf

http://shop.torresen.com/marine_diesel_direct/Yanmar/

Torrenson is good for parts etc.

Let me know what you find. I will use the information someday for sure.