The carb should have a choke pull-off that would open the choke once it fires up...assuming it's an automatic choke and not a manual/cable type. That adjustment is critical to get the engine running smoothly when the engine is cold. It has to let in the proper amount of air so it has the correct fuel ratio (a bit rich when cold). Too little air and it will run rich and belch black smoke out the tailpipe. Too much air and it will run lean and stumble/hesitate/die until the engine warms up. Once the engine is at full operating temp, the choke should be fully open and no longer affecting the running of the engine.