I had the same problems with bubbles seemingly originating in the RNV. I tried changing the little O-ring on the needle valve, but no better. I put zip ties around all the fuel outlets (nipples), but no luck. It turns out that I had inadvertently round down the tiny lip on one of the nipples, when my screwdriver ground up against it as I was trying to tighten one of the engine mounting screws.

Don't give up! Try the things I said above, and good luck! I was going nuts over this.