There are foundational items that all must be addressed to maintain any older equipment. The most important items for a small tractor such as an Onan Case are:
New fuel line SAE 30R7 1/4" and filter tank to carb.
New ignition switch. You must have full voltage transfer. If it has rust on a terminal, it is bad.
Clean Carb, see Hemlock Case Guy channel on YouTube, that is me.
Onan Intake sealed. See Hemlock Case Guy on Facebook.
To all that say that they added an electric fuel pump and have had no issue since then, I reply that I have cleaned and rebuilt the stock system and they have worked as designed when new since then.