Low ambient temps and venturi effect can cause throttle plate freeze-up of any accumulated moisture carried over from the engine crankcase vent tube.
This was a later vesion production modification that can be retro fitted to earlier models... They also modified the vent pipe with a cuff to the water feed pipe to help any freeze in that pipe, as a blocked vent can cause engine crankcase back pressure , with results of engine oil seals and tach drive leaks......
