Fuel Idle Mixture Screw with Washer and O-Ring. Fits: XS650G/H/SH/SJ/SK/SL (1980-84) with Stock Mikuni BS34 CV Carbs. Note: This Mixture Screw is 25mm in length, there are 2 different sizes that were used. Be sure to measure your old one to confirm this is the size you require before purchasing See following 48-5012 text.   Part #48-5011 $6.95/Kit

Mixture Screw Kit - Mixture Screw, Mixture Screw Rubber O-Ring, Blind Plug Washer, Spring and Washer. (Includes All Contents Shown). Fits: 1980-84 XS650G/H/SH/SJ/SK/SL Stock Mikuni BS34 CV Carbs. Note: This Mixture Screw is 20.5mm in length, there are 2 different sizes that were used. Be sure to measure your old one to confirm this is the size you require before purchasing Plug covers vertical re-cessed idle mixture screw & keeps out contaminants. O-Ring fits under metal Washer at bottom of mixture screw hole and the engine will not idle properly if it is not present - (O-ring is often disintegrated). These parts are not shown in service & parts listings as Yamaha did not want "emissions" related parts accessed, however adjustments were often necessary to get New bikes to run properly. Suggested setting position of the normally hidden mixture screw is 2 1/2 to 3 turns out from bottom.   Part #48-5012 $7.95/Kit