Steve

I'm in a mild climate here too - only 2-3 frosts a year but at times it gets pretty humid.

My 270 has the riser baffle still in place, but stuck in the open position (exhaust gases straight out).The only time I have experienced any icing up has been on warm-up on extra damp or humid days until hot.Otherwise having the riser open is no problem here.

You would be over-heating the manifold in warm weather if your baffle is completely gone though.