Yamaha Wr 450 F Owners Manual
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7 - 3 TUN SETTING Effects of the setting parts on the throttle valve opening 1 Pilot screw/pilot jet 2 Throttle valve cutaway 3 Jet needle 4 Main jet ÅClosed ıFully open 1/2 3/4 1/4 1/8 1 2 3 4 Åı Main system The FLATCR carburetor has a primary main jet. This type of main jet is perfect for racing motorcycles since it supplies an even flow of fuel, even at full load. Use the main jet and the jet needle to set the carburetor. 1 Jet needle 2 Pilot air jet 3 Needle jet 4 Main jet 5 Pilot jet 6 Pilot screw
7 - 4 TUN SETTING Pilot system The FLATCR carburetor is manufactured with a pilot screw. The pilot screw adjustment ranges from fully closed throttle to 1/4 open throttle. Main jet adjustment The richness of the air-fuel mixture at full throt- tle can be set by changing the main jet 1 . * Except for USA If the air-fuel mixture is too rich or too lean, the engine power will drop, resulting in poor accel- eration. Effects of changing the main jet (reference) Å Idle ı Fully open Standard main jet#150 *#160 1/4 1/2 3/4 +10% #150 –10% #160 #140 Åı
7 - 5 TUN SETTING Pilot screw adjustment The richness of the air-fuel mixture with the throttle fully closed to 1/4 open can be set by turning the pilot screw 1 . Turning in the pilot screw will make the mixture lean at low speeds, and turning it out will enrich it. * Except for USA NOTE: If the idling speed fluctuates, turn the pilot screw only 1/2 of a turn in either direction. To optimize the fuel flow at a smaller throttle opening, each machine’s pilot screw has been individually set at the factory. Before adjusting the pilot screw, turn it in fully and count the number of turns. Record this num- ber as the factory-set number of turns out. Effects of adjusting the pilot screw (reference) Å Idle ı Fully open 1 2-1/4 turns out 2 1-1/4 turns out 3 1-3/4 turns out Standard pilot screw position1-3/4 *1-1/2 (example) 1 1/4 1/2 3/4 +5% –5% 1 23 Åı
7 - 6 TUN SETTING Pilot jet adjustment The richness of the air-fuel mixture with the throttle open 1/4 or less can be set by adjust- ing the pilot jet 1 . * Except for USA Effects of adjusting the pilot jet (reference) Å Idle ı Fully open Jet needle groove position adjustment Adjusting the jet needle 1 position affects the acceleration when the throttle is 1/8 to 3/4 open. 1. Too rich at intermediate speeds Rough engine operation is felt and the engine will not pick up speed smoothly. In this case, step up the jet needle clip by one groove and move down the needle to lean out the mixture. 2. Too lean at intermediate speeds The engine breathes hard and will not pick up speed quickly. Step down the jet needle clip by one groove and move up the needle to enrich the mixture. Effects of changing the jet needle groove position (reference) Å Idle ı Fully open 1No.5 groove 2No.3 groove 3No.4 groove Standard pilot jet#45 *#48 Standard clip position No.4 groove 1/4 1/2 3/4 +5% –5% #48 #42#45 Å ı 1/4 1/2 3/4 +10% –10% 1 23 ı Å
7 - 7 TUN Jet needle adjustment The jet needle is adjusted by changing it. * Except for USA The tapered sections of all jet needles have the same starting positions, but the needles are available with different straight-portion diameters.Standard jet needleOBDUT *OBDUQ OBDUT - 4 Clip position Diameter a of straight portion Effects of changing the jet needle (reference) (Diameter of the straight portion) Changing the diameter of the straight portion adjusts the air-fuel mixture when the throttle is 1/8 to 1/4 open. ÅIdleıFully open Relationship with throttle opening The flow of the fuel through the carburetor main system is controlled by the main jet and then, it is further regulated by the area between the main nozzle and the jet needle. The fuel flow relates to the diameter of the straight portion of the jet needle with the throt- tle 1/8 to 1/4 open and relates to the clip posi- tion with the throttle 1/8 to 3/4 open. Therefore, the fuel flow is balanced at each stage of throttle opening by the combination of the jet needle straight portion diameter, and clip position. 1/4 1/2 3/4 +10% T –10% S U Åı SETTING
7 - 8 TUNSETTING Carburetor setting parts * Except for USAPart name Size Part number Main jet Rich *(STD) (STD) Lean#170 #168 #165 #162 #160 #158 #155 #152 #150 #148 #145 #142 #1404MX-14943-41 4MX-14943-91 4MX-14943-40 4MX-14943-90 4MX-14943-39 4MX-14943-89 4MX-14943-38 4MX-14943-88 4MX-14943-37 4MX-14943-87 4MX-14943-36 4MX-14943-86 4MX-14943-35 Pilot jet Rich *(STD) (STD) Lean#52 #50 #48 #45 #42 #404MX-14948-08 4MX-14948-07 4MX-14948-06 4MX-14948-05 4MX-14948-04 4MX-14948-03 Jet needle Rich (STD) Lean#DUQ #DUR #DUS #DUT #DUU #DUV #DUW5TJ-14916-D1 5TJ-14916-DR 5TJ-14916-DS 5TJ-14916-DT 5TJ-14916-DU 5TJ-14916-DV 5TJ-14916-DW Jet needle Rich *(STD) Lean#DUM #DUN #DUP #DUQ #DUR #DUS #DUT5TJ-14916-DM 5TJ-14916-DN 5TJ-14916-DP 5TJ-14916-D1 5TJ-14916-DR 5TJ-14916-DS 5TJ-14916-DT
7 - 9 TUN Examples of carburetor setting depending on symptom This should be taken simply for an example. It is necessary to set the carburetor while checking the operating conditions of the engine. Symptom Setting Checking At full throttle Hard breathing Shearing noise Whitish spark plug Lean mixtureIncrease main jet calibration no. (Gradually)Discoloration of spark plug → If tan color, it is in good condition. If cannot be corrected: Clogged float valve seat Clogged fuel hose Clogged fuel cock Check that the accelerator pump oper- ates smoothly. At full throttle Speed pick-up stops Slow speed pick-up Slow response Sooty spark plug Rich mixtureDecrease main jet calibration no. (Gradually)Discoloration of spark plug → If tan color, it is in good condition. If cannot be corrected: Clogged air cleaner Fuel overflow from carburetor Lean mixture Lower jet needle clip position. (1 groove down) The clip position is the jet needle groove on which the clip is installed. The positions are numbered from the top. Check that the accelerator pump oper- ates smoothly (except for rich mixture symptom). Rich mixture Raise jet needle clip position. (1 groove up) 1/4 ~ 3/4 throttle Hard breathing Lack of speedLower jet needle clip position. (1 groove down) 1/4 ~ 1/2 throttle Slow speed pick-up Poor accelerationRaise jet needle clip position. (1 groove up) Closed to 1/4 throttle Hard breathing Speed downUse jet needle with a smaller diameter. Slow-speed-circuit passage Clogged → Clean. Overflow from carburetor Closed to 1/4 throttle Poor accelerationUse jet needle with a larger diameter. Raise jet needle clip position. (1 groove up) Poor response in the low to intermediate speedsRaise jet needle clip position. If this has no effect, lower the jet needle clip position. Poor response when throttle is opened quicklyCheck overall settings. Use main jet with a lower calibration no. Raise jet needle clip position. (1 groove up) If these have no effect, use a main jet with a higher calibration no. and lower the jet needle clip position.Check air cleaner for fouling. Check that the accelerator pump oper- ates smoothly. Jet needleClip Groobe 7 Groobe 6 Groobe 5 Groobe 4 Groobe 3 Groobe 2 Groobe 1 Leaner ↑ (Standard) ↓ Richer * SETTING
7 - 10 TUN EC720000 CHASSIS EC71P002 Selection of the secondary reduction ratio (Sprocket) Secondary reduction = ratio It is generally said that the secondary gear ratio should be reduced for a longer straight portion of a speed course and should be increased for a course with many corners. Actually, however, as the speed depends on the ground condition of the day of the race, be sure to run through the circuit to set the machine suitable for the entire course. In actuality, it is very difficult to achieve set- tings suitable for the entire course and some settings may be sacrificed. Thus, the settings should be matched to the portion of the course that has the greatest effect on the race result. In such a case, run through the entire course while making notes of lap times to find the best balance; then, determine the secondary reduction ratio. If a course has a long straight portion where a machine can run at maximum speed, the machine is generally set such that it can develop its maximum revolutions toward the end of the straight line, with care taken to avoid the engine over-revving. NOTE: Riding technique varies from rider to rider and the performance of a machine also vary from machine to machine. Therefore, do not imitate other rider’s settings from the beginning but choose your own setting according to the level of your riding technique.Standard secondary reduction ratio50/14 (3.571) SETTING Number of driven sprocket teeth Number of drive sprocket teeth
7 - 11 TUNSETTING EC72N000 Drive and driven sprockets setting parts * For CDN, EUROPE, AUS, NZ and ZA * For AUS and NZPart name Size Part number Drive sprocket 1 (STD) *(STD)14T *14T5NG-17460-00 9383E-14215 Part name Size Part number Driven sprocket 2 (STD) *(STD)48T *48T *49T 50T *50T *51T 52T *52T5GS-25448-50 5NY-25448-00 5NY-25449-00 5GS-25450-50 5NY-25450-00 5NY-25451-00 5GS-25452-50 5NY-25452-00 EC721002 Tire pressure Tire pressure should be adjust to suit the road surface condition of the circuit. Under a rainy, muddy, sandy, or slippery condition, the tire pressure should be lower for a larger area of contact with the road sur- face. Under a stony or hard road condition, the tire pressure should be higher to prevent a flat tire. Standard tire pressure: 100 kPa (1.0 kgf/cm2, 15 psi) Extent of adjustment: 60 ~ 80 kPa (0.6 ~ 0.8 kgf/cm 2, 9.0 ~ 12 psi) Extent of adjustment: 100 ~ 120 kPa (1.0 ~ 1.2 kgf/cm 2, 15 ~ 18 psi)
7 - 12 TUNSETTING EC722011 Front fork setting The front fork setting should be made depend- ing on the rider’s feeling of an actual run and the circuit conditions. The front fork setting includes the following three factors: 1. Setting of air spring characteristics Change the fork oil level. 2. Setting of spring preload Change the spring. Install the adjustment washer. 3. Setting of damping force Change the compression damping. Change the rebound damping. The spring acts on the load and the damping force acts on the cushion travel speed. EC723001 Change in level and characteristics of fork oil Damping characteristic near the final stroke can be changed by changing the fork oil amount. CAUTION: Adjust the oil level in 5 mm (0.2 in) incre- ments or decrements. Too low oil level causes the front fork to produce a noise at full rebound or the rider to feel some pres- sure on his hands or body. Alternatively, too high oil level will develop unexpectedly early oil lock with the consequent shorter front fork travel and deteriorated perfor- mance an characteristics. Therefore, adjust the front fork within the specified range. ÅAir spring characteristics in relation to oil level change ıLoad ÇStroke 1Max. oil level 2Standard oil level 3Min. oil level Standard oil level: 130 mm (5.12 in) Extent of adjustment: 80 ~ 150 mm (3.15 ~ 5.91 in) From top of outer tube with inner tube and damper rod fully compressed without spring. Å