"Part throttle hesitation is much reduced at 5 turns on APT. Still some small lag, not a crisp throttle at cruise or off idle yet."
Still too lean at 5 turns (APT maxxed out) indicates low fuel level, or possible a vacuum leak someplace. This would also explain not being able to get the engine to idle without blocking off the bypass air.
I would imagine your "builder" used the wrong fuel inlet seat, and float setting at the low factory spec.
I would install the correct needle/seat assembly, and set the float at 9/32". This will raise the fuel level and richen things up everywhere without changing jets and metering rods.
I'm also betting that the secondary throttle plates are leaking too much air around them, or the linkage is preventing the primary plates from fully closing. Aside from a vacuum leak, or WAY too much timing at idle, no other reason it woln't idle down on the stop screw.
I see a LOT of folks having very similar issues as you are having. Quite a few of those carbs end up here for custom tuning. Near 100 percent of them have the float too low, and leaking air around the throttle plate(s). 100 percent have the wrong needle/seat assembly, and nearly that many have bent power piston hanger arms.
Folks, this isn't all that difficult, but it does require exact precision. Just making one little mistake like not pulling the idle tubes and cleaning the crud out of them will get less than satisfactory results when the carb is placed in service.
Installing the wrong parts will do the same thing. This is why one of the first things we recommend, is to install one of our kits, to get the correct parts in the carb, and up to par for modern fuels. Once that is done, and float set correctly, we can start to effectively troubleshoot to find any issues that you are having........Cliff
