The choke is only used when starting a cold engine. When doing a cold start, the choke should be closed to limit the amount of air going in. ... Once the car has warmed up, if the choke does not open fully, the restriction in air may result in reduced power.

How do I know if my choke is open or closed?

When the choke butterfly is allowing the most air flow, without restriction, it is open. Like a door. Open lets things through. when the choke is restricting the flow of air, it is closed.

Is the choke supposed to be up or down?

If you have the NT carburetor the choke is on (closed) when the lever is up. If the engine isn't running it doesn't make any difference where it is. The choke should be off (open or down) when you're riding. Just remember to shut off the fuel petcock when the bike is parked.