Cycle News - Archive Issues - 1970's

the front forks wh ich now seem out dated in comparison to the rear suspension. Other th an t he Mo nocross suspension a nd the Nogu chi/Yamah a works paint job, the bi ke is quite sim ilar to th e p resently avail able 25 0 YZs. T he engine is the sam e except for so me small p orti n g changes to he lp broaden t he power a lit tle. T h e p o wer is wi d e a nd to rq uey, but the engine has such a ligh t internal ro t atin g m as s tha t it re vs very q uickl y. The trick is to try and shi ft early so the engine wi ll almost lug an d pull the bike smoothly , but that isn 't easy. In th e first three gea rs th e Mo nocross w ill accele ra te faster than it ca n be sh if ted. A n ew 4. 60 x I 8 D un lop Sports Se n ior w ith ferocio us knobs sticking o ut of it everyw here, now co m es on the 250 YZ , but wh ee lsp in is still vicio us an d i t's h ard to get enoug h traction to bring the fron t end up u ntil you hit fo u rth gear. T he Y Z engine is a marvel. It's d erived fro m the original 01'-1 e ngi ne of seven ye ars ag o , and it is still one o f the strongest and most competitive 250 engines aro und. It is now a highly stressed GP e n gine thoug h, an d it requires co n tin u o us upkeep and replacement of parts, that wear o ut quickly. The piston ne eds con sta n t replacement, and the gearbox has a rep u ta tio n for being unable to survive a seaso n o f co mpet itio n. Pro pe rly maintained, it's one of the best. The Ya maha factory teams in the U.S _ a nd Europe ha ve rece ived a bike , dubbed the Mark II, which has a completely ne w engine design and is m ad e almost totally ou t of magnesi um . Magnesi um also replaces many o f th e a lum in u m parts on the b ike itsel f to he lp b ring th e weigh t down to the F1M limit o f 194 pounds. Our test b ike wei gh ed in at 2 16 wi th a half tank of gas . Like th e prod uctio n Y Zs it uses the same hu b s, fo rks, tank and other componen ts. T hi ngs like the b ra ke backing p lates are magn esium . bu t th e majority of co mponen ts are alu min u m . St eel item s like the ax les a re dr illed h oll o w an d bo lt h ead s arc dis hed out. O K, so we 've told yo u all this neat stuff, b u t w hat is it li ke to rid e the m o st techn icall y ad vanc ed an d j ust plain fast motocross bike in the worl d? In one word, bitc h in '. Bu t fi rs t , yo u have to pretend you 'r e five feet ten inches ta ll and y o ur na me is Hakan be ca use it's going to frighten you before you ever get on it. It's th e tall est motocross bike t here is . m o re th an tw o in ches tall er th an a H usky a t the sca t and m ore th an si x inches high e r than a n El sin o re a t th e st eering head. The seven in ch es o f travel in the m on o sh oc k reall y jacks th e rear e n d up , and th e seven and a h alf in ches o f fork tra vel throws the front end wa y o u t. The works Front fender loo ks' like a snow pl o w , totally hiding th e tire fro m view, and t he st ra p pe d do wn alu min um tank is big fo r those 45 mi n u te full thro ttle m o te s, Tony d id n ' t even thin k h e could get o n it , let al one ho ld -it u p. When you do ge t o n it, tr ying to balance it from one side w ith a pointed toe, the m ono sh o ck won 't even compress but st ays top p ed out. Like all Yamah as , p ull the enriche ning valve up on the Mikuni car b an d it starts ea sily. T here really isn't a lot of cylinder co m p ressio n. T h e e ngi ne takes about a lap to w arm up b ecause th e ch ro m e pl a ted a lumin um cylin der rea lly keeps things co o l. As you cr uise around o n th e b ike slowly, you notice that e ve ry t h in g o n t he Mon ocross is very p recise. Clutch, shifter, brakes and steering all work exactingly and wit h see mingly no effo rt w hatsoever. It 's unsettling at first, because you can ' t feel th ings li ke t he shift lever moving when you want to c h an ge a gear. The tr avel is ap prox im a tely o ne -h alf in ch and the lever requires no pre ssur es other than a foot being under o r over it. Now 's the t im e to st art gassi n g it. Hang your toe under the shift lev er a nd turn th e throttle on. Every time y o u tum the throt tle off th e gearbox will snap itself into th e n ext highe r gear. It's n eat, bu t before yo u know it you 're going faster th an you w ant and there are some bad whoop-de-des co m ing up. Beller b ack off the th rottle, maybe even da b the brakes a little to get slowed down to a reasonable tank slapping speed, o th e rw ise you just know you're goi ng to endo . As soon as the b ike's weigh t shifts to the front e n d though, and yo u 're in wh oop-des, t he back end start s bouncing up and d o w n . Amazingly it keeps tr acking a straight line and won't co m e aro u n d, b UI you ha ve to h an g o n f or dear life to stay on top o f it. May be we're do in g something w ron g. It sure does n 't hand le li ke a no rmal mot o c ross b ike. That in stan t w e accide ntally ge t back o n the thro ttle whi le bou nci ng thro ugh the w hoop -di es and th e weight of th e bike sh ifted back. T h e rear e nd sure felt sm oo th . Beller !!O rou nd a n d try it aga in, bu t th is lim e leave th e throt tle on a lillie. Hey , that fee ls ev en smoother, m ay be w it h e ven a litt le more throttle.. .And th at's th e se c re t. Ea ch lap as y ou !!O b ack and run tha t whoop-d e-do sec t io n a little faster, m ak ing th e rear sus pe n sio n wo rk h arde r eac h t ime , th e b ett er a n d sm ooth er th e Mo n ocross w orks. Fin all y y ou've b uilt up enoug h confidence t o tackle it with fu ll throttle and it handles ev e n better yet. I t's t he sa me sec tio n y ou used to run on your o ld bi ke , much slower, w orkin g the throttle o n a nd off to keep the fr o n t e nd airborne an d th e rear e n d b ouncing al ong b eh ind. T he "Mon osh oc k is to tall y 'di ffer en t and req u ires yo u to handle a rough section like it 's a na t piece o f gro un d, ac t u ally ac cel era tin g across it with t he p o w er on fu ll, b ut not trying to keep the fro nt end air born e . The fro nt w he el takes ca re o f it self, skimming across th e to ps of the ruts a nd whoop-des as the rear wheel d oes all t he w o rk, A ll th e while yo u 're riding the bike, th e d amping is c ha nging it self to suit th e track con d it io ns. O n smoo th , ro lli ng b umps it stays fir m so the bike won ' t wallo w. The sharp imp act of a hard b um p a t hi gh speed causes sp ring loaded va lves in th e oi l p assag es o f t he mon osh o ck to open up q uickly an d absorb the j o lt wi th minim al da mping , th en they close b ack up as th e swing a rm slows its im p ac t speed a nd reaches its lim it o f travel. Return da m pi ng is also p ro gr essive, d epending on such factors as whe ther rider weight is o n th e re ar o f t he bike o r n ot, an d if th e rear wheel is in con tact with t he grou n d . R o ugh gro un d in a high speed tum is eve n m ore fun because you can leave the pow er o n , o r pl a y wi th t he thro ttle w itho u t worry ing about th e rear slidi ng o u t . This is w he re th e bi ke re ally am azed us, be cause it seemed li ke we could n' t get th e bike to reac h a limit in fast turns , th e rear wheel j ust st icks. Of th e fo u r o f u s wh o rode th e Monosh o c ker re all y hard, a nd we all have pro licenses, T ony w as the only one to fall off the b ike o nc e in th ree d ay s o f riding. He didn't do it on o ur test bike, but on a sp a re bi ke that hadn't been set up properly ye t. It was a p p ar e nt to us th a t we were com ing nowhere ne ar the li mits of the b ike's h an dl ing p o t ential on rough gr ound. , T a kin g j u m ps on th e Monocross was re ally fu n be cause no ma tter how h ard th e landing impact was the m onosho ck was a ble to take it , with the first p ar t of com p ression being very soft then be coming progressively stiffe r as th e su sp en sio n w as used up . T h ere was never a ny rebound actio n . I t felt like the bike w as landing on a p illow. If th ere is any lim it on j u m ps, it's in the front forks which h ave a tr emendous amou n t of rake to com pe n sa te for the long travel in the rear. When landing, the front wh ee l ca n only b e a f ew inche s hi ghe r than the rear, o r when it slaps d own qui ckly the fo rks will try to flex o u t in stead o f co m p re ss. The ex tre m e ra ke is needed th o ugh to h elp the hand ling wh en the rear en d is not compresse d , otherwise handling becomes d an gerously ' q u ic k wh en the th ro ttle is sh u t off on ro ug h gro un d or wh en braking fo r a t u m. Many people d oin g th e c u rren t sw ing arm m odifica ti ons to their b ikes fai l to take th ings like f ork rake int o co n sid era tion . The b ike handles so we ll that it is impossible to get you rsel f into troub le w ithout w an tin g to. Maybe that's wh y Pier re Ka rsmakers can rid e h is Mo nocross so w ild ly, headin g it ever y direction but straight , an d st ill stay up o n both w heels. The b rakes o n the Mon ocross Y Z are the b est. Yes t hey're ve ry se ns itive a nd lo ck up easy, to o easy fo r m o st p eople, b u t if you d on 't ha ve th e sk ill to use th e m without killing the engine or be ing flipped over the b ar s in a turn the n you shou ldn' t be o n the b ik e in t he first place . Near the: end of a long m oto , it sure is nice to know that you only have to remove one weary finger fro m t he righ t grip and lay it on the lever to ge t the bike stopped. With most o th er bikes you w o uld have give n up using the front brake lap s ago. T he rea r brake is non -floatin g, but the n full fl oatin g h u bs have seemed to go o ut of fad li ke t hree inc h tr avel rea r suspensions. T he Monosh oc k has the t he oretically p erfect rear brake geome try w ith st rai gh t lines from the swi n g arm , br ake rod, a n d ba cking pl ate t orque ar m al l in tersecting at t he same p ivot poin t : the swi ng arm ax le. Wheel hop fro m usin g the rear brake is nonexis tent. T he lo nger we rode t he Monoc ro ss the m o re we liked it. The height of t he bi ke is fo rgot te n and b ec ause it is ligh t, it 's easy to keep flin gin g around w ithout getting ti re d . Even w he n laid over to the h andlebar s fo r a slow berm turn the re is almos t no work involved. It defi nitely made a better ride r o f all of us who rod e it, an d t he faster you ride the Mo noc ross, the better it works. The only co n cl u sion that can be d erived fro m the tes t of the 2 50 Mo n ocro ss is t hat this is the one bike that will to ta lly change the sport of m o to cr oss. We won ' t say it's better than th is bike, or that one, be cause at this stage of the game the re isn 't any othe r b ike ca n really co m p a re with it . No other manufacturer will readily admit that t hey have a long travel rear suspension d esign that really works righ t fo r a w hole race, and h ere Yamaha is wi th a b ike that d oes. • j > Specifications Engi ne Bore and St roke D isplaee ment . • . Com pression rat io Horsepower . . . . . Torque . • . . . . . . Car b ure t ion . . . . . Ignit ion Transmissio n • _. . .. •. . .. . .... 5 . 70mm x 64 mm . . .. . • . . •. . . • • •. .. . . . . 246c e (act ual) 7 .4 :1 • • . • • . • . . . . (appro x .) 28 @7500 . . . . . . . . . . . (app rox .) 20@70 00 . . . . . . . . . . • . . . • .34 mm M ikun i COl speed, w ith mu lt i-plate w et clut ch Dimensions Wheelb ase Seat height . . . . . . • . . . . . Hand leb ar height .. . . ... . Ha ndlebar width Footpeg h eight , Gro und clearance Weight . ... ... . . . . .. • . .. Weight bias __ 56 .5 i ns. . . . .. .. . . .. . . . . . 34 -36 i ns. . . . . .. .. . . •. . .. . . . 4 3 in s. 36 ins. . .• . . . . . . . . . • . . . . . 13 i ns. 10 ins. . . . Iw /half tan k fuel) 2 161bs. 94 Ibs. fro nt/ 12 2 Ibs. rear 29

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