Why does 2002 honda xr50 run better with choke at half way instead of off

The jets are a little clogged or gummed up. Clean the carburetor jets and it will run better with the choke off. What happens is with the choke off, there is too much air and not enough fuel in the air fuel mixture because not enough fuel is passing through the jets but the same amount of air is always allowed. With the choke on, you are restricting the amount of air flow which helps to correct the fuel/air mixture into the engine. To clean the jets, you will remove the float bowl from the bottom of the carburetor, there will be at least two jets (sometimes up to four) in the bottom of the carb, remove both jets and use carb cleaner and compressed air to clean them. DO NOT USE any type of tool because it can scar the jet passage and change the fuel flow as well. Also be sure to use the proper screw driver to remove the jets since if you damage them it can also change the fuel flow. Also, when removing the jets, be aware of any washers or spacers that may be in place when removing. Good luck