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/127125
The YZ's airbox is .la rger, as is the intake boot, to improve air flow to th e carburetor. Water-cooling passages ar e now mostl y internal , whi ch eliminat es th e need for excessive hoses. The cylin de r head ha s no coo la n t inl et. Coo la nt p a sses up throu gh the cylinder a nd into th e head di rectly fro m the water pum p . T he left radiator is 20m m longer. T he clutch is beefed u p with 8m m larger d ia me ter pla tes. th at n o w rota te o n n eed le ro ller bearing s ra the r than bu sh in gs. The cl u tch push rod a nd - lifter-cam have been mod ified to ligh ten cl u tch- lever pul l. T rans m issio n cha nges incl ude re d uced p rim a ry redu ction gea r ra tios, a nd closer gea rbo x ra tios. T he shift sha ft ha s been mov ed ba ck 16m m and raised 5m m in order to use a longer sh ift lever to p ro vide smoother shifti ng actio n. T he ki cksta rter sha ft is m oved inboard 5m m to narrow th e m o tor in th e footpeg a rea . The o n ly thing unchanged abo u t the Yamah a 's white-painted frame is the 28° ra ke a nd 4.7-inc h trail. The rest is a ll- new, including a n a lum- . inurn steering stem, larger steerin ghead pipe. beefed up motor mounts, a reinforced front dowruube a nd la rger d ia me ter but thinner sidewa ll seat-support tubes. T he sw ingarm pivot has been lowered 5mm in the frame to mi ni m ize cha nges in chain tension a nd red uce to rque effect o n the rear suspens io n. Ten mill imeters has been ad ded to the swingarrn 's len gth , giving the YZ a longer 58.3inch wheelbase. Un like th e Honda. Suzuki and Kawasak i, the Yamaha does no t have any kind of detach able rear sub-frame section. The Monocross rear suspension has a more progressi ve ris ing rate than befo re, a nd the Bra ke Acti va ted Suspension Sys tem (B.A.S.S .) is now h istory. Since th e rear brak e is now a disc, ra ther tha n a drum , an d has new Monoc ro ss linkages, and swi ngarm length a nd location, Yamaha tra shed th e B.A.S.S. design , which used to cha nge th e shock's co m pres- sion damping when the rear brake was applied. The shoc k is built by Yamaha using Ohlins spec ifica tio ns . The pi ggyb ack reservoir shock features externa l rebound a nd co m p ressio n da m p ing adj us tments. U p fro nt the Yamaha now has a ca rt ridge type fork mad e by Kayab a, similar to Honda 's Showa ca rt ri dge forks. Th e Ka yaba unit h a s 16 d amp in g ex te rna l re bo u n d adj us tme nts. Other ch assis cha nges include sm a ller a nd lighter hubs, meatier Iootpegs, new handlebars an d a new sea t th at cl im bs further up th e gas tank. On the track Both pow er a nd sus pe nsion have been im proved immen sel y o n the YZ. The m o to r sta nds o ut the most with stro ng p u ll o ff th e bottom and potent m idrange; but top en d isn 't a ny th ing to rave a bo u t. The power o ff th e bot tom is reminiscent to th e tractor-pulling power o f th e 1985 YZ250 but has more strength o n top. This m akes th e new Yamaha very easy to ride a nd p leasant to live with. Not o n ly does th e YZ have th e power to ge t you from o ne turn to th e next as quickl y as a n yth ing in it s cla ss, th e YZ's mot or is ext reme ly easy to roost arou nd with, on or off th e track. T hrott le resp onse is predi ctable and spo t o n, making th e Yamaha co n troll abl e o n slick, dr y an d hardpacked tra cks, a nd pl enty strong enough to ta ke adva ntage o f perfect traction on moist and tac ky tracks. T he Ya ma ha shifts better than ever. The longer and reposi tioned shifter has 100% improved feel , a nd co mbi ned wit h the ligh ter clutch pu ll, missed shifts are nea rl y a th ing o f th e past. Kick starti ng th e Yamaha is n o easy task. T he kick sta rter lever is very short , a nd doesn ' t turn th e motor o ver enoug h in just o ne stro ke, because yo ur foot h its th e peg an d th e lever ca n' t go past the foot peg o n th e down stroke. It tak es a bunch of quick jab s o n th e lever to get the Yamaha fired up. Different porting specs, a modified YPVS and a simplified cooling system are j ust some of the changes made to the now extremely potent motor. The 1988 YZ250 is the best YZ Yamaha has produced in years. It's pretty much race ready right out of the crate. Test: 1988 Yamaha YZ250U Time for a change By Kit Palmer Photos by Kinney Jones If th ere's one motorcycle that was due for major renovation it was the Yamaha YZ250. Over the past few years, the YZ has seen relatively minor changes, and, because of this, the YZ has fallen slightly behind the times when comd h dorni d p~re to t e om~nant an high-tech Honda and Kawa- 6 sa ki MXers. But times have ' changed and Yamaha is looking to get back into the running with one of the most .radically altered 250cc MXers of 1988 - the YZ250U. Last year's YZ250 was a slightly refined version of the not-so spectacular 1986 YZ250, bu t the 1988 YZ250 is all-new from the knobbies up - no major parts are interchan• geable with the '87 model. The 1988 bike has an identity all its own. It has all -new, extremely eye- ca tc h i n g st yling, a co m p le te ly ~evamped, seyen-port motor, a b~frer frame, Iine tuned suspension components and refined erg o nomics. The water -co ol ed , now silverpainted motor, is different in every sense of the word. Port design is new with wider transfers and a straighter exha ust route, and a new intake port ' has been added, angled directly down into the crankcases. The Yamaha Power-Valve System (YPVS) is positioned 5mm lower in the cylinder to produce a more efficient (straighter) exhaust-port. shape, and the YPVS governor opens 3mm wider. Compression ratio has been raised from 8.58-10.23 :1 to 8.72: 10.65:1.