DOT4 to DOT 5 Silicon

[McCabe-Thiele (Ted)]

The A series positive crankcase system consisted of a spring loaded valve with a rubber diaphragm inside this was connected directly to the inlet manifold iirc. The other side of the valve was connected by a pipe pipe to one of the two  crank case side covers with a simple tubular oil separator type device combined with the cover. My understanding is it was introduced to meet emission regs back in the day - effectively any vented gas from the engine was recycled into the combustion system. If you undid the oil filler cap the engine revs would drop & it would often stall.

[K2-K6]

That's likely a side effect of SU type carb in that the slide is vacuum operated which also controls fuelling, drop in vacuum and carb slide should go down, even though traditional air leak on engine side ordinarily results in increasing revs.

So conflicting outcome based on equipment peculiarities. The carb damping oil will stop flutter and control rate of change, but will ultimately settle to where vacuum dictates. 

I used oil viscosity here to trim fuel "mapping" profile in setting them up, the SU type that is.