David:
It sounds like blocked air passages in the "other" carb set. The most likely: the tiny one that goes from the itty-bitty brass hole at the air horn end, down and forward to the emulsifier tube. These get blocked from non-use, mostly, and from other debris, especially if they were run without air filters.
To clean them, remove the emulsifier tube and the jet needle (that's the brass hole in the middle of the carb throat, where the needle slides in & out), by tapping gently down with a plastic something-or-other to avoid damage. Then, use a small (22 AWG or smaller), flexible mechanic's wire and push it in the little brass opening, then down about 3-4mm, then forward to the emulsifier tube area. You'll see it arrive in there, with a strong light. Run it back & forth to scrape out the deposits, then pull out the wire and spray some carb cleaner through the hole, watch your eyes! It will go everywhere...
When these tubes are partially blocked, the midrange runs real rich and the idle screws have little or no effect on the low speed mixture, pretty common.
The carbs: check on the top of the front flange of each carb set, see if the stamped-in number is the same, at least before the final letter (which indicated mainjet changes). With the exception of the cable-type carbs, almost all "K" series carb parts will fit all other "K" series carbs. Within the early K0, the first few months of production had some different cable mount nipples on top, different cable (shorter #4 cable, and even the 4-in-1 and 4-2-1 arrangement cables). All floats should be set at 26mm after the sandcast cases disappeared. The sandcast ones did have some 24mm settings (like my friend Jim's bike), but Honda's reps told us to lower it to 26mm to reduce the plug fouling tendencies of the K0. We were required to do so on all bikes that came in for any warranty work, and got paid for it, $8!
So, then, we racers immediately went to 24mm to get the extra high-end HP and low-end torque, heck with the sparkplugs!
