Re: Yanmar 1GM10 won't start.
Go to the other thread on Yanmar starting and try the technique of warming it on compression then using full throttle. If that won't start it, then look for something else. Diesels rarely run perfectly one day and fail the next, so don't fear the worst just yet. Possibles:
Fuel is contaminated - high pressure filter (the one on the engine) partially blocked
Air intake is blocked (the foam self-destructs over time)
Fuel shut-off is stuck in shut-off position or the cable has come adrift from the arm on the FCU
Valves stuck open - maybe due to slight mis-rig of the decompression lever - a 'love tap' with a rubber hammer on the rocker cover could be the fix for this, otherwise pull the rocker cover and see if the valves are moving through full range as you crank it.