Rick,
Good point, and certainly worth checking.

The Evo comes out of the box with the carb already mounted, but it's quite possible it was factory mounted not-quite snug enough.

I've had some engines that leak air around the needle valve (poor quality o-rings). Those get cured with a bit of fuel tubing around the needle. I don't think he's leaking air around the needle (engine is too new), but who knows for sure.