Yes I have the new version with the straight pipe and the rotating muffler. And yes the nut is 14mm. I was planning using a 14mm deep socket like dessartrat suggested. Then a 14mm open ended wrench on the outside nut.

My needle valve fits nicely inside the cowl. In fact, I had to add a 3/4" piece of piano wire with an L shaped bend in order to extend it out of the cowl. I made it so the L is barely out of the cowl and I do not need to fuss with it in order to take the cowl off. I don't even need to flex the cowl in order to get it over the wire. I'd say the wire ends up being 1/8" past the opening I drilled into the cowl. That ended up working out great. I'll try to upload a picture of it when I get home.

The reason mine fit inside the cowl is probably because I did not rotate the carb like some of you did. I just redrilled a hole for the throttle linkage opposite the one that was standard.