As stated above the idle speed screw is the one with Phillips head. The slow speed air/mixture screw is the slotted screw.
With the engine warm turn in the Phillips screw 1/8 turn and speed up the idle a bit. Then screw the air screw in 1/8 turn at a time until the engine speed increases, if it doesn't turn the screw out 1/8 until the idle increases when you have the idle at its maximum turn the air screw in 1/8 until the engine just starts to slow down. Then turn the phillips screw out in 1/8 increments until the idle returns to normal. Note : Idle speed for these engines is quite high at about 1500-1800 rpm. Not a slow phut-phut-phut.
Then go to Shell and fill the tank with Shell VPower 95 and let that run through the system over time. Can repeat if you want. VPower has extra additives for cleaning as does Bangchak S91 or S95