While the engine was out of the Wonderbus a couple of days ago, I peered down into the throat of the right Kadron/Solex carb and noticed that it looked blackened. The left one was clean.
I puzzled over this while I was doing my duties to the engine. Then it occurred to me: the last time the engine was out I installed a hose from the aftermarket oil filler nozzle to the top of the right carb's air cleaner. This as a way of recycling crankcase blow-by emissions.
But I would not be happy, no I would not, if the funky fumes were to clog up my carb, with nasty dirty gunk and glop.