Assuming you were running DQ264/K93/128/CD1/60 jetting, not sure why you had a problem in the rain. I say this because I have never run that set up in the rain. Since you mentioned low end I would suggest that either the idle jet or atomizer were responsible for the hiccup, or maybe the needle height. On the other hand could it have been water getting to carb? The only way to find out would be to change either jet and see what the response was. Of course this is after the fact and not much help.