Last summer I replaced air, oil, & fuel filters which helped immensely. But I still have a problem. If there is more then 5 gallon of fuel in the tank it keeps stalling on me. It ruins great for a few minutes then it starts bogging down if you try to move. It will restart immediately and run great for a few more minutes. I thought maybe I was stirring up the tank when fueling it but the last time I filled it I let it set for 2 weeks before starting it. That didn't make a difference. Once I get down to about 5 gallon in the tank it will run great again with no problems. My only guess is a fuel pump but this seems like weird behavior.
I don't know how the tank is vented but you might try loosening the fuel cap and see if it runs ok like that.
Or as soon as it stalls remove the cap to see if there is suction in the tank. With a full or nearly full tank of fuel it should be gravity fed to the pump. Trying to remember, I think the 1845 has a camshaft operated pump that suck through one filter and then pushes fuel through the second filter to the inlet of the injection pump. Could you tee in a pressure gauge to see the pressure goin into the inlet of injection pump?
I'll take a look & see if my pressure giraffe will fit it. I just checked at the cap yesterday & there is a vacuum but it still runs the same with the cap lose. I also noticed there is two fuel filters & I'm pretty sure I only change one of them.