I have only recently bought my SZR so I'm still in the process of finding out it's idiosyncrasies.
The engine breather pipe feeds directly (via a coarse filter in the pipe) under the secondary carb diaphragm. This is a bizarre way of supplying what normally is atmospheric pressure to the lower part of the diaphragm. Supplying atmospheric pressure to the diaphragm allows the piston to lift when a lower pressure exists above the diaphragm, which in turn supplies more fuel/air to the cylinder. This lower pressure is drawn from the intake venturi, at the throttle butterfly and the lower pressure increases as the vacuum increases depending on the throttle position, drawing the piston up.
The Teikei Y26 carb appears to draw from the engine breather pipe when the engine is running on the primary carb. I can only assume Teikei have allowed for the pressure balance due to the air pulse from the crankcases by the size of the air feed above the diaphragm and the mass of the diaphragm and piston assembly
What does happen in reality is that the secondary piston flutters up and down (you can here it rattling, I thought it was the timing chain at first) if the idle speed is set too low. The fluttering is due to the air pulses from the crankcase breather pushing the piston up and down. None of this really matters though as the secondary butterfly should be totally closed on idle as the primary carb is supplying the mixture to the engine up until around 5mm of its opening.Apart from not fouling the air filter with crankcase oil and fumes, I really don't understand why they use this method of crankcase breathing and I really don't get operation of the secondary carb this way as the crankcase pressure will rise with engine revs but someone much cleverer than me must have an answer.
I still think the original poster should be looking around this area for his problem. Here's a pictorial on the carb cleaning................I think the oily gunge in this has been caused by overfilling the oil tank............... http://bultaco.proboards.com/thread/502 ... ikei-y26pv
PS I hadn't read your post edfmaniac before I submitted mine - we're singing from the same songsheet
Bill H - have you checked the breather pipe is neither choked or split?