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Sorry bout the bad pic. This is the screw you need to pull out. It is called the Idling jet carrier in my book. Right behind it, usually comes out with it, is the idling jet, just small brass tube. This is also called the low speed jet and affects idle and part throttle big time. Pull out jet, has TINY hole, clean with carb cleaner and compressed air, even that air in a can will work. Now piss carb cleaner into hole where jet goes, now compressed air. Got your safetly glasses on right?? You can pull out idle mix screw as well and do the same if you wish to get idle passeges good and clean. Idle mix screw should be bottom very lightly and turned back out about two turns to start with. There is another jet like this on the other side of carb in same spot, this is the one for the primary side.
The big main jets very rarely have issues, holes are big enough they are hard to plug.
Could also pull top off carb, and see what is in bowl. Water, gunk will settle to bottom of bowl, jet are not right on the bottom to keep em from sucking up the gunk, but if gunk gets deep enough will start getting into jets, engines run poorly on water.
Really, if you pull idling jets out, pull top off, now carb clean thru various jets adn clean out bowl, you have fixed 95% of carb issues. Accel pump can cause probs too, it is outside carb and easy to change if leaking.
Keith