These bikes do not really have a "choke".
A choke restricts airflow to make the fuel mixture richer.
When you close the "choke" on our bikes it has no effect on airflow, It adds more fuel to richen the mixture.
So if it runs better with the choke on, then you were probably lean.
I agree with Dan, you may have dirt or partly blocked fuel passages, start with a good dose of seafoam.
Cold air being denser will have the effect of leaning the engine. You may have just been on the verge of lean when it was warm, now that it is cold you are over the edge.