I put a piece of clear silicon tube after the filter into the carb, and at the gas tank. After running a while 20-30 min, I saw bubbles that got worse until foam then it quit, no air at the tank output.
Next I removed the tube from the gas tank and put some gas with cleaner in a can and ran again. No bubbles from the can but again bubbles at the carb. So it appears that either there is a air leak between the input to the gen through the filter to the carb.
Unfortunately the great engineers at Onan never left enough hose to replace the filter without dropping the gen. So now I have to remove the gen to remove the green cover to replace the filter and hose.
The new setup I will run the hose from the pump which I will mount on the outside of the case and drill a hole for the hose up front and it will be a straight shot to the filter and the carb, so I will be able to see all the fuel flow except in the main gas tank. Which was clear, no bubbles. I'm guessing it was one of the fittings or hose clamps. I will connect the carb to the filter and run the hose out the side, then mount the gen then the pump then finally run the hose to the mane tank.
If they had human engineers at Onan they would have put a small cut out or door at the fuel pump and left enough slop to remove and replace the filter, but they want you to go to a dealer to get it serviced.
So ordered a new fuel pump, filter and hose. Total cost under $55
Looking at the fuel pump I pulled out, it was doomed to leak.
One end has a welded right angle connector with a hose barb adapter screwed into that.
The other end has a welded straight adapter with a right angle adapter screwed into that and a metal(rusted) tube screwed into that and then it bends 90 degrees and 4 inches to another hose barb.
I think mine was leaking air at the metal tube adapter, its discolored where it screws into the right angle adapter.
I'm going to replace both ends with just a straight through hose barb adapter, no metal tube as soon as the hose gets here. I got the filter and pump today.