K2 - starting with the basics:
Slow jet #40 Keihin or #42 Keyster in carbs of type 657B.
Air screws set between 1/2 turn and 1-1/2 turns is their whole range - OUT is RICHER, IN is LEANER. Turns beyond either of these extremes doesn't change any more in that direction. Stock is 1.0 turn out with Keihin #40 pilot jets and brand-new carb bodies: it becomes less turns with age because each successive bottoming of the screws widens the seat in the soft body of the carb - go gently!
Mainjets: if the bike was made before 3/1972 they were #110, which was often too rich. After 3/72 they became #105 (and stayed there until the roundtop carbs disappeared).
Float level: before 3/1972 builds some of the K2 bikes had brass floats (mine did, originally). If yours are brass, there are tiny slivers of metal sticking up, adjacent to the notches on the bowl gasket surface, that are to be used as the float 0 reference - not the float gasket surface. However, if the floats are plastic, this little edge will be missing: then the float reference surface (sans gasket) is the 0 height reference. Floats should be set at 26mm height for starters. (The posts for the float's pin changes between these 2 carb types, altering the float height.)
Slide needles: the OEM version are numbered #27201 and the clip goes into the 4th notch from the top (blunt end) of the needle. If yours don't have this number on them, they are not Keihin needles.
Needle valve (in the throat of the carb) for Keihin are different from those used for Keyster's fatter needles. They must be changed in sets or the Keyster needles will stick in the needle valves. If the Keyster needle valves are installed then the Keihin needles will rattle around from looseness even when the slides are fully closed, so fuel gets sucked up the mainjet too early in the throttle sequence, making everything uncontrollably rich.
The Keyster brass parts ALL run MUCH leaner than the Keihin parts: they are not properly designed for use in these carbs (never were), but have often been installed anyway. The Keyster parts will make the engine run very lean if the above jetting numbers are used (which usually come in their kits). Typically this lean: if all else is set to usable points, the mainjets must be in the range of #125-#140, depending on the other mods done to the engine. Compare that with the stock #105-#110.
I won't get started on trying to use pod filters on this bike: they don't work well, nor can they be made to. You will have to accept some serious compromises to use them, including short sparkplug life.
