So I've been scratching my head. Figured I'd see if anyone can think of something I've missed. My 580k with the 4-390 NA, fires off right away, but then dies after idling for like 2 seconds. Then it has to crank for probably about 7-8 seconds before it fires again, then runs fine. If you shut it down and start it back up the same day it starts fine, but let it sit over night and the start issue comes back. Can't find any leaks, nothing seems to have air getting in or out of the system.
There is a check valve in the return line at the fuel tank it could be leaking pressure off when machine sets for awhile.
The fuel lift/primer pump could also be the culprit. Built in check valve not holding on the suction side - you can only replace them with a new one. Not very expensive.
My 1st step would be the fuel filters, THEN.. lift/supply pump.. THEN retighten all the connections from the fuel tank on forward..