Hi,
I also just got a couple of wankels so I have no experience to offer other than yes, there is a wankel plug you are suppose to use, however that is not the reason fuel is pouring out the carbs. My guess would be that since they are nearly upside down and oriented below the fuel tank, they are drawing fuel and thats what you are seeing. I have a magnum 52 mounted inverted on a Cermark Javelin II that does the same thing. I have to hold the plane upside down (engine right side up) and start it this way, then I flip it over after I start it. It's a pain but what you gonna do???
Good luck,
FJ