I would read the choke section in my Carb FAQ to make sure the choke really is working right. It should only be about 1/8th inch open when closed.. 1/2" might make a difference when real cold.

Also read the idle screw adjustments to see if yours is out of whack.

I'd check that stuff and what stock87 mentioned and post back with the results.

-Scerb

http://www.scerbfab.com/carb_faq.html