Some thoughts: If you are not seeing bubbles in line from tank to (regulater) needle valve then I would think all is well there. Bubbles are only between needle and carb, right? Pretty much isolates it I would think, to needle valve leakage. Ok, start engine open needle valve as many turns as it takes to get a rich run. If it takes more than 2 to 4 full turns needle is definitly leaking air. It should run peaked at about 1 1/2 turns and rich about 2 turns. One thing that at times works is to put a 1/4 inch length of fuel line on needle just above the threaded area. If this is a new engine this should not happen but if old then perhaps O ring is dried out, replace it. Also be sure the nipples that fuel line connects to at regulator and carb are tight.