Assuming you are using fresh fuel:

Did the engine tend to konk out at the beginning of the throttle or the end (wide open) ?

Did you adjust your idle with the plane right side up or upside down?

How was your transition? Is there a difference with the engine is right side up or up side down?

If you open the throttle slowly up and down, one click at a time, was there any sag in rpm or even konks out after a few seconds? Was that with the plane right side up or up side down?

Looking at the plans of the US+, the carb centerline with an upside down engine is quite a bit lower than the tank, and the tank is pretty far back from the firewall. I am assuming you set up the plane per US+ plans.