We have a 1985 vintage Nanni Kubota 4.110HE, also discontinued. We've had success getting parts
and various information from Waterway Power Center in Annapolis
, MD. We got an engine
manual from another place in Ft Lauderdale back in 2002, but they no longer deal with Nanni Kubota.
If I were you, I'd call Waterway Power Center in Annapolis
410-266-0590, explain what you have and ask if they can get you an engine manual. The web address is: http://www.waterwaypowercenter.com
FYI, here's the intro from their website: "Waterway Power Center was created in 2000 to import and distribute Kubota/Toyota based Nanni Diesel engines for the east coast of the USA".