Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/128109
(YZ1 25 ) t im e t o swit ch its atte ntion ba ck to the YZ 12 5 and YZ 25 0 two-s tro k es, a s well as t h e YZ 8 5 (t h at w e 'll fea t ure next w eek , w hic h w ill i nc l ude a m i n i r i d i n g im p r es s io n ) and g ive them a com p le t e ma keove r. A f te r a ll , Ya m aha k n ow s tha t t he c ompeti t i o n w i ll i n e v i t abl y c atc h up - and perh ap s p ass yo u u p - if you sit idle fo r t o o lo n g . A lth o u g h ne i ther t he Y Z 125 n o r t h e YZ2 50 look rad ically different though they d o have distinctive new a p p e a r a n c e s - Yamaha made so many interna l changes to t h em that you certainly cou ld qua lify the m as " a ll -new" b ikes . Pretty much the only th ing s carried o ver f ro m last yea r's YZs are the fr on t f ende r and fr ont n um b e r p l a te . T h e YZ 125 an d 2 5 0 sh ar e many of th e same c h assis an d suspension c ha nges , while t akin g on t h eir o wn motor modification s. Th e 200 2 YZ426F di d n't g et as m an y c ha nges as ei t h er of the twost ro k es, though it di d get so me durab ili ty -type upd ates to its powerp lant , as we l l as takin g o n a fe w of th e sa me c hass is c ha n ges as th o se o n th e YZ 12 5 and 2 5 0. A s far as th e 2002 YZ2 5 0 F , Yama ha h as yet to divulg e mu ch in form a ti on about th e " l it tl e " t h u m pe r, but d on 't ex pect a wh o le lo t o f c ha nges . W e k now th at its c hassi s w ill get th e same treatment as th e 426, but m oto r m ods ar e st ill a secret. Starting w ith th e YZ 125, p erha ps the b igg est n ew s h e r e i s th e swap fr om a s ix -spee d transm i s sio n t o a fi v e -speed tran sm iss ion , all' Ho nda 's CR 125 R. Yam ah a f elt t ha t w ith the b ike 's in c rea sed ho rse po w er fo r ' 0 2, t hat a five-spee d gearbox wo ul d enhanc e th e YZ 's r id eability. Yamaha sa id th at special attentio n was pa id to the gea r ratios b etw een secon d an d third g ea rs - where 125s ar e usually ridden th e most - so that the rid er will ha r d l y n o t i c e th a t he has o ne le s s g ear to work w it h . W e 'll see . Wh en i t c o m e s t o th e YZ 125 ' s mot or , c h a n g e s t o th e cy li n de r 's scav enging a n d ex ha ust ports , a n d c a r b u reto r , are sai d to ma ke th e YZ fee l l ik e a "sma ll 250 rather than a big 125 - li k e it u sed t o . " In oth er w ord s , Y a ma ha m ad e an e ffo r t to g ive t h e n ew 12 5 mo re b ottom- en d without sacrificing p ower elsew h ere . Yamaha was unable to provide us yet w ltlt much Infonnatlo n regarding changes to the 2002 VZ250F, but the bik e does get some of the same chassis changes as the YZ1~ and 250. Wh en it co mes to th e YZ250 's motor, a fe w chan ge s wer e made, such as tweak in g the pow er -va lve, updating the ignitio n, fi ne-tuning th e ca rburetor, going back to carbon -fi be r reed -valves, and in serting a spacer b etwe e n the cylinder and the carburetor. Both the YZ 125 an d YZ250 share numerous chassis changes . Perhaps the most notable is the frame 's back bone, which is now elliptical in shape , wh ich Yamaha cla ims inc rea ses lateral r ig id ity whil e d ec reas ing lo ngi t udi n a l rig id ity . Yamaha feel s th at some flex in th e fra me is a good t hing. as lon g as you c an c o ntrol the amou nt of fl e x , an d p u t th e flex w here you w ant it. A ll of the 2002 YZ s ( b ut n o t t h e YZ85) ge t " w o r k s" -t y p e wide r fro nt h ubs , w h ich is said to im p ro v e ha n dling an d sta bi l ity , ma i n l y t h r ou gh fl at corners . T o a c h ieve an even a n d m or e co m fo rta b le la y out, Ya ma ha lowered t he fr ont and rear sections of the seat area, w h ile keepi ng t he ce nter section seat - heig ht th e sa me . Als o , to m ak e the Y Zs mor e ro omy , Ya maha m o u nted t he ha ndle b ar s 10mm forward. The ba rs th em selves are a lso 10mm lower in h eight, but si nce th e handl eba rs are p la c ed fa rther forw ard , where th e mounts are 5mm h igher, th e act ua l o v erall height of th e handlebars over last year's YZ is j ust 5mm lower. As you can t ell vi sually. Ya m a ha com pletely red es igned the now-bl ack a ir b o x o n th e YZ 125 and 2 5 0 . Not only is t he air b ox not w h ite an ymo re (too m a n y c o m p lai n t s a bo u t whi te being im p o ssi b le to k eep cl ean ) , bu t the air bo x al so fea t u res a new shape a n d new a ir i n let lo ca tions. Yama h a g o t rid o f t he in lets beh ind th e seat t hat we re o n th e re ar fe n der , wh ich m eans no m ore wh eel /fender cont act w he re th e inlet " bo x" used to h an g d own underneath th e fender. But p rob a b ly t h e best n ews of a ll fro m Ya maha is that none of th e new YZs will see a pric e in crea se for 2002 . Also , Ya maha will continue its lucrat ive c onti nge ncy program for 2002. Cylinder: Exhaust and thi rd scavenging ports' shapes are changed. Piston: Position of the dent pin on the piston ring is ch anged, and piston ring width is cha nged from 2.15mm to 2.35mm. Carburetor: Engine-sid e bor e diamet er has been increased from 38mm to 40mm, though the center section of the bore remains at 38mm. Needle and needle jets are changed . Radiators: Larger radiator (one m ore core row) . Radiator louvers featur e four louvers instead of three. Silencer: Th e silencer is 25mm shorter and is mounted in an angle to clear the rearbrake caliper when bottomed, thus elimi nated the need for "dents" in the silencer body. Ignit ion: Th e newly designed 8·bit m icro com puter COl unit is sm aller in size. Transmission: Th e YZ's transmission is now a five-speed, as opposed to a six -speed Shift cam is lighter and m odified to improve shifting 1001 1001 3 0 /13 = 2 .3 0 7 28/16 =1.866 2 6/ 17 = 1.529 27/2 1= 1.286 26/ 2 3 = 1.130 24/24 = 1.000 27/ 12 =2 /250 .31 /1 7 =1.824 2 9 /19 = 1.562 24/19 = 1.26 3 25/ 23= 1.0 8 7 N /A Gear Ratios 1st 2nd 3rd 4th 5th 6th (YZ2 50 ) Power-Valve: The YPVS valve shape is changed, and a plate has been added to the rear of the torsion spring to increase closin g force by the return spring , improvi ng air tightness. Reed-Valv e: Reed material has gone back to carbon fiber . Intake Manifold: A 4.5mm aluminum spacer and O.5mm gasket have been added. Kick Starter: The kic k- starter arm has a new shape, and the kick-shaft diameter has been reduced from 20mm to 18mm. Shift Fork: The shape is the same , but engagement of the shift fork and shift fork shaft is strengthened. Exhaust Pipe: New shape to enhance engi ne changes. Silencer: Uke the yz 125, the silencer is mounted at an angle to clear the rear-brake caliper. Ignition: COl magn eto and rotor are newly designed , and crank inertia mass has been increased. Th e COl uni t is. like the 125, sma ller in size, but has been repo siti oned to below the fuel tank. (YZ426F) Lubricat ion: Engine-oil amount has been reduced from 1700cc to 1500cc . Piston: Piston-h ead thickness has been increased. Ca r buretor: A cap o n the throttl e si de is added and th e carburetor c over seal constru ction is revised. The hot -starter hole-diameter is increased. Crankcase A ssemb ly: Th e crankcase pivot shaft hole inside diameter is larger. (Yama ha cl aim s this change improves the bike 's overall handling.) Clutch: The primary driven gear spring window shape is changed , as is the flat -end rivet length (reduced by l.5mm). The shapes of both ends of the absorber are changed , as the small diame ter coil is eliminated. ~lliJ&~~ll~ @ ~lHlMm fUTI1l~~~ (YZ 125 /YZ2 50 ) Frame: All new. The main pipe section of the frame (underneath the fuel tank ) is now elli ptic all y curved to increase lateral (side -to -side) rigidity, wh ile slightly reducing longitudinal rigid ity. The alum inum sub-frame now uses fully square sections. A ir Box: All new. The sealing method between the intake boot and the air box has been changed for im proved sealing, and new air inlets eliminates the need for the rear fender inlet, and that means no more underhang in the rear fender and fender/tire contact. ErgDnomics: The fuel tank, seat, side covers and airbox are reshaped to achieve a flatter layout (seat height. however, is the same). The handlebar height has been lowered IOmm and positioned 10mm forward : however, the more forward position ing of the handlebars raised the enti re handleb ar unit 5mm, so the actu al height of the handlebars compared tc last year's YZ is act ually 5mm lower. (YZ 125/2 50/2 50F/4 26F) Swingarm : Wherever perm issibl e, the thikness of the swingarm has been reduced . Chain Adjuster: Th e chain pull er is slightly shorter to redu ce weight. Unkages: The link mounting bolt is changed and a stopper is added to the link side. The pivot shaft diam eter is changed from 17mm to 18mm. , Shock: Th e rear shock length has been changed from 48 7mm to 492 m m , and the internal settings have been changed. Fork: The fork internal s featur e a new two -piece piston for incr eased oil flow (to improve mid -stroke performance). Front-Wheel Hub: A wider, "works"-like front hub is used. The bearing span of the front wheel hub is increased from 50mm to 70mm. Rear Brak e: The diameter of the rear disc has been increased from 240mm to 245mm. Rear-Brake Caliper: A support bra cket has been added. CN cu e I e n e _ S • J UNE 20, 200 1 37