You might be able to remove just one but it will be much easier to pull them both to do the job. Make sure it isn't a float issue and not coming from that fitting. You can put a piece of clear tube on the bowl drain and hold it up along side the carb and open the drain. Fuel will fill the tube to the level in the bowl unless the float isn't closing. The bike needs to be upright to try this not leaning over on the side stand.

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