last
this is how my bike looks like with the new 29CR's.
Tried them out for the first time at the race and almost took the out and re-installed the old 27's.
Finding a steady idle speed was almost impossible, engine would either die or stay uo at 4K rpm.
A fellow racer gave me the tip of the day: these CR's (at least on a 500) need to have the air screw almost shut off! he reccomended ti close them to 1/2 a turn from fully closed (usually it's 1.5 turns) and hey presto! excellent idling and low speed response!
Still need to work on the needles and main jet but I am 90% there with the jetting.
I'll confirm your finding regarding the CR airscrews. I'm running about 1/4 to 1/2 turn on my CR26s (CB400F). It has to be this rich to get a decent, but not great, idle. You'll find, though, that the airscrew has most of its impact on the 1/4 throttle region. You run the screw in to get a good idle but at the expense of a low throttle rich misfire and sooty pipes. Dropping the needle can help this.
This is fundamentally due to the poor design of the idle circuit. Keihin decided to keep all of the main and idle circuits in the jet-block, a replaceable section of the carb body that sits just below the slide. I presume they did this for ease of manufacturing, but the unfortunate consequence is that the idle circuit enters the port on the upstream side of the slide edge. Thus the idle circuit doesn't see full engine vacuum and it resultingly acts more like a venturi-driven main circuit, ie. ineffective at low airflow, and, even worse, far too effective as airflow increases. When the CR evolved into the FCR, the idle circuit moved to the downstream side of the slide, so it's obvious that Keihin realized just how poor a design compromise they'd made.
A true fix would require a substantial effort to redrill the idle circuit. Not sure it's even possible. Screw it, I'll idle the damn thing at 2500 and wipe the pipes occasionally.