THat is the idle mixture screw, It controls fuel mixture at an idle...
If you are cutting out at High RPM's you'll need to rejet. Put in a larger main Jet. You can get them at your local dealer/Atv shop.
Take the bowl off and its the bigger round slotted brass think in the center of the carb. Look on the side, get a bigger number for richer mixture...
Check out the jetting sticky..
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