The jet needle (amongst other components) contributes to CX/GL fueling across ~50%-100% throttle opening.
Here’s your Honda CX500, GL500, CX650 or GL650’s slide piston with the jet needle visible coming out the bottom:

The jet needle and jet needle come as part of a set from Honda, part number 16012-415-671 (eBay US). At the top of the slide you have a small plastic piece:

Looking down from the top:

It lifts out – note the little O-ring that runs around the middle:

Looking down from the top now you should be able to see a slot for a flathead screwdriver:

Unscrewed:

The underside of that piece:

The jet needle will now be able to be lifted out:

Top of the jet needle – note that there aren’t any grooves to change a clip into like some carbs have; to adjust the mixture here you need to use shims:

Tip of the jet needle:

It has the characters 2 5 D inscribed around it:


The underside of the slide piston:


And you’re done. If you’re following the carb cleaning guide, go back to the main carb cleaning page for the next step.