Normally no need to bleed these engines as they have an electric fuel pump.
First, there is a solenoid that must engage before the engine will start. If this solenoid doesn't engage (you should hear it go clack), the engine will turn over forever, but never start! This solenoid is what shuts down the engine should the safety systems activate. Therefore, if you have a fault in the safety systems it will not engage. You can wire it open during your attempts to start the gene, but never run the engine this way.
Absolutely a must to use the glow plugs EVERY single time you want to start the gene, unless it has been running for a while. That means between attempts to start it. Around 15 seconds should do, no more than 25, ever.
The electric fuel pump should make a clicking sound, but if it doesn't you can check if it is working by just pulling off the feed line to the injection pump for a second.
It would help a great deal if you knew the model#, such as MDKD. Also, many parts you need for the engine can be had from a Kubota dealer for a fraction of the cost from Onan, but you will need the parts books from both companies (available online free).
I just rebuilt my MDKD, having the generator end serviced and replacing the diesel engine. After a ton of research, I decided to rebuild rather than replace because nobody makes as good or as simple a generator today. A transformer and a bunch of relays, available at almost any auto parts store, are the whole control system. No massively expensive PC boards to fail.
Good luck.
