Left carburetor rich, unaffected by idle air screw

If you’ve been keeping up with my progress, you’ll remember that I recently rebuilt my carburetors and re-installed them on the CB350, but that I was having some trouble tuning them, and that some lightish smoke (with black condensate) was coming out of the left muffler.

I did some further investigation today, using the old pull-one-spark-plug-lead-off method to run the bike on one cylinder. While running on the right cylinder alone, the bike’s idle was in fact controlled by the idle speed screw on the right carb. However when I ran the bike on the left cylinder alone, the idle speed was entirely unaffected when I manipulated the screw. I could screw the idle screw all the way in or remove it entirely and the bike ran either way.
This would seem to indicate that there’s some sort of condition on this carb that is causing fuel to make it through even when the idle air jet is pulling nothing but air. There’s likely a rich condition. ┬áThat COULD also explain the smoke from the left muffler.
Because I’m not seeing anything coming out of the overflow tube for this carb, I have a hunch that the floats are set too high in that carb. When I have some free time I’m going to try adjusting it downward to see it that helps.

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