Well you've had some answers, I guess, but none of them address the true problem. Look at the picture. The carbs are below the nacelles which means gravity is pushing fuel into the carbs. It's unlikely that you'd ever get them to run too well that way since the mixture will change as you consume fuel, but if you flip the plan over, you should be able to get them to start and run. The long term fix will be to rework the mounts so you can get the carbs on the centerline.