Keihin 22mm Carb (People 150)

[John in PA]

Anyone know of a source for an overview of Keihin stock carb function?  i.e. what the various adjustments do, and where fuel mix changes occur?  I've worked on Dellorto, Bing, and Amal motorcycle carbs, but these are new to me.  Is the pilot screw an air screw or a fuel screw (does adjusting that screw add and remove air or fuel (various carbs do it one way of the other)

Also, what is the 1/2 inch long brass nipple coming out of the bottom of the carb near the float bowl gasket, with a hose to the intake manifold.  Is it a float bowl breather or vent?  Can I plug it, or does it need to breathe?

(Cross post from People 150 page--no response there)

[dickdes]

http://www.bonneville.se/nedladdning/Hur%20man%20jettar.pdf   This refers to a Triumph Bonny ,the basics are the same .Word of caution when drilling the slide ,small increments save having to get a new one.

[dickdes]

http://www.carbparts.com/keihin/needles_tuning/keihin_tuning.htm ,a little more in depth tuning info

[John in PA]

I think the PB series Keihin carbs are very different from the more sophisticated carbs found on Triumphs and Japanese big bikes.  For one thing, it's a butterfly carb instead of a slide.  Also needle jet arrangement is different. 
Does anyone know if the pilot screw is an air screw or a fuel screw.  In other words, does counter clockwise turning add air or fuel to the slow mix??