If it's not starting despite normal cranking speeds, it's either fuel
starvation or perhaps lack of compression. The first is easy to fix, bleed things out properly it should fire. This could require bleeding the system up to and including the injectors.
Poor compression will require a rebuild.
A major caution here - make sure your raw water intake is closed for extended cranking - otherwise you may find water in the engine/oil from backing up in the exhaust
system. This can cause more damage and further inhibit starting.