One thing I just thought of is if it could be an air leak. A number of years ago I had a similar problem with a .40 glow engine where one of the carb screws came out and the engine had a very high idle and no matter what I did with either of the needles couldn't get it to idle down. Then I noticed the missing screw and all was well.

Like I said, mine without any adjusting on the mixture screws will idle reliably at 2100 or so, I'm sure I can get the idle down further once I start peaking the needles.

Mike