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/126982
of all t he 1988 VZs. The frame. suspension. motor and styling are completely different. New bikes: 1988 Yamaha YZ MXers By Kit Palmer H ighligh ting ·Yainah a 's fleet of 1988 m o tocrossers is the middle-of-the-line YZ250, which sports new, eye-catch in g stylin g, a re designed frame, r eworked motor and updated suspe ns io n co rnp oThe YZ250 is an all-new motorcycle .f rom top to. b o t tom ; no major parts are totern ents, 14 cha ngable betw een th e 1987 and '88 YZ250s. Ch ange has not been as rad ica l with th e o ther m ot o cro sser s in Yamah a's 1988 YZ mod el line. The '88 YZI25 maintains 1987 styling , but has eno ug h internal cha nges to qualify as a new motorcycle. The YZ490 is ba sicall y th e sa me a ircoo led big -bo re as th e model offered last year, excep t for o ne not eworth y cha nge - th e forks. On the ot he r end of the di splacem ent spec tru m is th e YZ80, which feat ures mot or and chassis refin em ents. Man y cha nges ar e fou nd withi n the a ll -new YZ250's motor. Like th e YZ1 25, the 250 has a new, seven port design. T he extra I?on is a.n inta ke port th at feed s d irectl y In to th e cra n kcases. Th e Yam ah a P o we r Val ve System (YPVS) is resh aped and posi tioned 5mm lower to p ro vide smoo ther exha us t gas Qow. Tra ns fer po ns are wid er a nd the exha us t port IS stra ig h ter. T he cylinder head has less volume to in crease compressio n rati o. Ca rb ure tio n is still handled by a Mikuni (as is th e case on a ll th e new YZs). The exhaust pipe is resha ped to co mp lime nt th e portin g a nd YPVS cha nges, a nd a la rger a irbo x and intake boot are now used. Cooling was a major co ncern a t the Yam aha factor y. T he cylinder head no longer has a coo lant in let, but coo la nt now passes up th rough th e cyli nder a nd cases di rect ly fro m a larger capaci ty waterpurnp, T h is design red uces the a mo u nt o f rad ia- tor hoses. The left sid e radiator is now 20mm longer. The transmission and clutch o n th e YZ250 a lso feature a few cha nges. Clutch pl at es a re 8mm larger in diameter a nd now ro tate on needl e roll er bearings in stead o f bushings. A new ro u ting of th e clutch cable . a nd a redesigned cl u tch p us h rod a re designed to lighten cl utch pu ll. The five-speed transmission has d iffere nt, clo ser gea r ratios, a nd th e sh ift sha ft is moved back 16mm a nd u p 5m m in th e engine cases. The cha nge was mad e to improve shifting feel o n th e lever, leading 10 more positive gea r selec tio n . Ch assis and sus pe ns io n cha nges are pl entiful. The rak e a nd trail a re the same, but a ny th ing else . havin g to do with th e fram e ha s been com pletely a ltered. It 's designed to be sto nger by reinforcing certa in areas, suc h as th e steering head pipe, th e front downtube a nd sidewall sea t-s u p po rt rub es. Th e bi g gest cha nge to impro ve handling is th e lowerin g of th e swi ngarm pivot 5m m , a nd th e relocati on o f th e p ivot forwa rd in th e fram e. T h is minim izes cha nges in cha in ten sion, th us red uci ng to rq ue effect on the rear suspension. The swinga rm itself is 10mm longer. Mot or mounts bolts a re larger to reduce vib ration. Un like th e H onda, Suzuki and Kawasaki MXers, th e Yam ah a d oesn 't hav e a removeabl e, rear su bfra me sectio n. Other chassis cha nges incl ude th e swa p to a rear d isc brak e from a drum design ; new stra ig h t-p u ll spo kes; lighter hubs; beefed up foot pe gs; a redesigned sea t a nd different bend handlebars. The big news in th e suspens io n department is th e swit ch to cart ridgedesigned Kayaba fork s, sim ilar to th ose used on the Honda a nd Suzuki MX er s. All th e new YZ mod e ls . (exce p t the YZ80) feature thi s change. In th e rear , the Monocross linkag es a re revised. The new linkag e, a long with the relocation o f the swingarm pivot a nd th e cha nge to a rear dis c brake, mean th e Brak e Actuated Suspe ns io n System (B.A.S.S.) is no lon ger need ed . Th e s hoc k is a Yam aha-built Ohlins-t yp e whi ch features valving cha nges. Ch an ges to th e YZI25 ar e mostl y refinements. The motor features larger inta ke portin g, a lar ger reed -