So next time you have the engine running, pull each decompression lever one at a time and see if there is a difference between cylinders. If there is no change or not much of a change on one cylinder, that cylinder has in issue, Rings, injector or valves. Then next time you start the engine just decompress the one BAD cylinder.
If all are good each cylinder will sound like the next. Then
I found that if one cylinder has bad compression
, it will prevent the engine from starting. Could also be a bad injector or miss adjusted valves.
Mine in the end was broken rings . From discussions here, there was a bad batch of yanmar
3gm30's from the early 90's that tended to break piston lands at relatively low hours. Mine did at 1100 hours. With luck yours will be a bad injector or valves needing adjusting. Also check for leaks
in the fuel system.