Join Date: Dec 2011
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I'm not familiar with the YSM8, but I'd be surprised if it has a choke -- most diesels don't. The T-handle that is commonly used on sailboats to kill the engine does look just like the choke control on old-fashioned carburated gas engines, but it actually kills the fuel supply.
If you've cut off the fuel supply and the engine keeps running, it's getting fuel via an unorthodox method (it's possible but highly unlikely that the fuel kill mechanism is broken). The fact that the engine is not responding to throttle control also indicates the same thing. If the governor has failed, removing the fuel should still kill the engine.
One good possibility is that the fuel being burned is not diesel, it's motor oil. This can happen if you overfill the crankcase. Also, if the rings are shot, they can allow oil past them which will burn.
Another possibility is that diesel fuel has leaked into your crankcase somehow, same effect.
Another thing that causes runaway diesel engines is accidentally putting gasoline in them, but that usually happens immediately, not after a minute or two.
So, two things:
1. what color is the exhaust (white, grey, black, blue?)
2. Check the dipstick and see if the level is high, or if the oil has been contaminated with diesel.