Yes, it does. It's the main jet needle, moving the circlip up causes the needle to set lower in the slide putting more of the needle into the hole of the main jet letting less fuel in, that is, it gives you a leaner mixture and your engine will run cleaner, that is, not burble. You'll have to experiment to find which slot makes the bike run best over the full range of your throttle. It's better to start with a lower slot and work up ( leaner ), you'll just foul plugs. Too lean and you'll burn a hole in your piston.
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