Mine 2000 tomos targa lx (that's for chris..lol) always needs the choke to start and i gotta let it warm a few before i run it when it's cold (under 50 or so). It seems to love hot weather the best but loses noticeable power in humid (foggy or rainy) conditions. But it always starts in two or three kicks at the most (sorry to admit i bought the "no-ped").
But, i have noticed on other engines with points ignition i've worked on that in humid conditions, the points get damp and it weakens the spark. But simply cold weather is a prob with either the plug or the choke as the other guys have already mentioned.
Too bad my carb doesn't have a mixture screw...i don't really understand why it doesn't unless they wanna make you buy jets in order to experiment. My nephew's go cart has such a screw and i adjust as i go in order to get the best mixture for that particular day...i guess that'd be too easy and now i'm rambling...
Best of luck,