Yamaha YZ250X 2022 Owner's Service Manual

ENGINE10-4EAM30598JET NEEDLE GROOVE POSITIONADJUSTMENTShould the engine be hard to run smoothly at in-termediate speeds, the jet needle “1” must beadjusted. If the mixture is too rich or too lean atintermediate speed operation, irregular engineoperation and poor acceleration will result.Whether or not the richness of the mixture isproper is hard to be determined by means of thespark plug and therefore, it should be judgedfrom your feeling of actual engine operation.1. Too rich at intermediate speedsRough engine operation is felt and the enginewill not pick up speed smoothly.In this case, step up the jet needle clip by onegroove and move down the needle to lean outthe mixture.2. Too lean at intermediate speedsThe engine breathes hard and will not pick upspeed quickly.In this case, step down the jet needle clip byone groove and move up the needle to enrichthe mixture.EAM30605RELATIONSHIP WITH THROTTLE OPENINGThe flow of the fuel through the carburetor mainsystem is controlled by the main jet and then, itis further regulated by the area between themain nozzle and the jet needle. On the relation-ship between the fuel flow and the throttle open-ing, the fuel flow relates to the jet needle straightportion diameter around 1/8 to 1/4 throttle open-ing, whereas around 1/4 to 1/1 throttle opening itrelates to the taper starting position and to theclip position.Therefore, the fuel flow is balanced at eachstage of throttle opening by the combination ofthe jet needle straight portion diameter, taperstarting position and clip position.Example:A. In case of being 0.5 groove leaner in relationto N3EW-3rd groove.a. Difference of 0.5 grooveStandard clip position No. 2 groove1A. Lean (larger diameter)B. Rich (smaller diameter)1. 1/8 throttle2. 1/4 throttle3. 1/2 throttle4. 1/1 throttlea. Main nozzleN3EW-3N3EW-4N3EJ-3N8RW-3