[embee]

Well, first I always recommend that you don't leave a bike (or any engine come to that) idling for prolonged periods "to warm up". It's not particularly good for the engine, it's spending a long time at the worst conditions (cold/part warm). Just start it, let it settle for 30sec or so to be able to ease most of the choke off, then ride away gently.

Having been running for quite a while, putting any choke back on will have quite possibly fouled the plugs. If so, it will be unlikely to start (carbon fouling simply conducts the electricity and the voltage never gets high enough to spark). That may be recoverable by removing the plugs and cleaning them or heating over a flame, alternatively fit some new ones. Plugs need to get to around 300C or so at the centre electrode to self-clean.

Once properly warmed up the idle speed should be around 13-1400rpm, what does yours idle at normally? If it's low then it can easily tend to stall.