Grace,
I'm not just sure where to start here.....
Most of the Champion units are gravity feed top tanks. What that means is that the float in the carburetor is designed to handle just the fuel pressure of the hydraulic head from the top tank. So, if your planned auxiliary tank is taller, it may overpower the needle valve that regulates the fuel level in the carburetor. That could be a disaster.
There are ways to work around this, but none are simple or cheap.
Then there is another problem. These are splash lube engines and so have no lube oil pressure. A quick look says that they do have a lube oil level safety, but you still should be in the habit of checking this regularly.
Best of luck with both the hunt and the generator.
Matt
