Search function success! I ran into the exact same problem as the OP!
A couple weekends ago, I had my 803a out in my driveway, running on the aux fuel connection from a full 55 gal drum in the garage. I was letting the machine run for a few hours (laundry day!) as part of my monthly startup, which I usually just run off the onboard tank. This day, however, I wanted to go off the AUX fuel connection as a test for longer-term power outages.
After running the main tank low, I switched to AUX fuel and the pumped kicked on, primed then filled the onboard tank and shut itself off - no issues. When I came back to check a short while later, I noted a slow drip of fuel from the corner of the set. I confirmed the aux pump had shut off, then opened the onboard tank to visually check for the fuel level: yep - full to the brim. I assumed fuel was siphoning (passively) from the drum to the tank, so I disconnected the aux fuel line and let it run a while longer to bring the level down.
I estimate the fuel level in the drum was approximately 2' higher than the top of onboard fuel tank. Unfortunately, it's not really practical for me to relocate the drum so that it stays below the fuel level in the generator, so I'm looking for solutions.
My first thought was simply to disconnect the fuel line after the tank fills, then reconnect it once it needs fuel again; however, frankly, at that point I may as well just use Jerry cans, since it's about as much of a PITA and requires me to be constantly messing around with it.
The second thought would be to add a manual shutoff valve so that I could leave the aux fuel line connected, but I'd still need to manually switch between normal and aux fuel, while also making sure the valve was in the correct position.
Kloppk's idea for the solenoid sounds like the ideal solution for me. Has anyone implemented this yet? Does anyone have a go-to source for these types of valves? I'm assuming it would need to be a standalone unit (i.e. with fuel fittings and an electrical connection) which could be fitted inside the set (likely as close to the aux fuel connection port as possible) and connected to the 24V supply to of the aux fuel pump?
Thanks!
J