It could be a few different things here....
Most likely like NW said your plugs are fouled, however you may need to re-adjust your idle also.
It may be time for a carb sync
also when you start your bike from a cold start, use full choke, however once it's running, slowly back that choke off until it's running on it's own without the choke on at all.
When I had a carb'd bike I only had that choke on for about 30 seconds or less, if it needed more time to warm up, I still backed it off until the choke was not needed anymore.
I never once fouled out a set of plugs in that bike!