Yamaha YZ125 Owner's Manual

Also see for YZ 125: Parts catalog Owner's service manual Owner's service manual Owner's service manual Owner's service manual

ENGINE8-2EAM30593EFFECTS OF THE SETTING PARTS ON THETHROTTLE VALVE OPENINGEAM30594MAIN JET ADJUSTMENTThe richness of air-fuel mixture with 1/2–4/4throttle can be set by changing the main jet “1”.1. Spark plug is too hot.Select a main jet having higher calibratingNo. than standard. (To be enriched)2. Spark plug is wet.Select a main jet having lower calibrating No.than standard. (To be leaned out)EAM30595PILOT AIR SCREW ADJUSTMENTThe richness of the air-fuel mixture with thethrottle fully closed to 1/4 open can be set byturning the pilot air screw “1”.Turning in the pilot air screw will make the mix-ture enrich at low speeds, and turning it out willlean it.EAM30596PILOT JET ADJUSTMENTThe richness of air-fuel mixture with the throttlefully closed to 1/2 open can be set by turning thepilot jet “1”. It is changed when adjustment can-not be made by the pilot air screw alone.A larger size jet results in a richer mixture at lowspeeds, and a smaller size in a leaner mixture.A. ClosedB. Full-open1. Pilot air screw2. Pilot jet3. Jet needle4. Diameter of straight portion5. Clip position6. Throttle valve7. Main jetStandard main jet #430Standard pilot airscrew position 2-1/4 turns outStandard pilot jet #40