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/127216
O'l 00 O'l ...... ~ 00 ~ v ..0 8 v ;:> o Z The ATK 406 combines simplistic design w ith ease of maint enance. It's available in MX or cross country versions; on ly t he suspension is different. Bec ause of it s lig ht weig ht, the 406 i s extremely easy to flick around in t he air or on the ground . It performs extremely well on the tra ils. Riding impression: 1990ATK406 Keepin' it simple Simplicity is written all over the 1990 406 ATK two-stroke. While the J apanese O EM's are spicing u p their off-road/ enduro bikes with water-cool i n g, power-valves a n d 16 single-shock linkage suspensions, ATK is sticking with I manyted waysolderthand uncornof th e plica of e past. Man y peop le, including th e eng ineers a t ATK, feel that off-road bikes are just ge tt ing too sta te-of-the -art for th eir o wn good. That 's wh y ATK decided to add th e 406 to its o ff-road lineupin mid- 1988. ATK wanted to p ro vide a n easy- to- ma inta in, reli able, yet co m pe ti tive mo torcycle for bo th o ff-road and mot ocross use. Fo r reli ability sake ATK settled o n an air-coo led. 399cc. single cylinder, piston port , case -reed valv e R O laX motor. Man y o ff-roa d riders a re not yet sold on th e idea o f water-cooled engines , especially for end uro usc. And th ose p eople do have a point. Despite h avin g it s ad va ntages. wa ter-coo led engines are more susceptib le to failure in end uro si tua t io ns tha n air -coole d c ngi nes . Bran ch es ca n eas ily p unc tu re radiators; bo tt lenec ks , as well as mudclogged rad iators. ca n ca use o verheati ng prob lems. a nd waterhoses can be ri pped. Pl us. wi th o ff-road riding. it isn' t uncommon to have to ma ke trai lside engine repairs and water-cooli ng ma kes th ese u nwa nted sto ps just that m u ch more comp li-ca ted and tim e co nsu m in g. especially if you' re raci ng. For red uced ma inten ance reasons, ATK o pted not to use a n ex ha ust power-val ve in th e Rot ax motor, in stead rel yin g o n its mid-sized, yet somew ha t bi g 399cc m ill to su p p ly th e torque a nd respectabl e top-end speed. As far as cha nges , th e n ew motor on ly has a few. But according to ATK. th e results ar e night and day. The first step was th e swa p from a 36m m Mikuni ca rb u re to r to a redesigned 38m m Ilat- slide ca rb, a n d th en a spacer was added to th e casereed-valve ind uction system. Both m odificat ion s wer e d esigned to in crease horsep ow er throughout th e pow er range. The Snorkel airbox o n th e ATK is o f un ique design. The a irbox and filt er eleme nt are mounted in front o f th e gas tank , on th e left s ide, with th e a ir in ta ke cu to ut behind th e front number pl at e. A sea led cha m ber funnels clean air down al ong th e frame's backbone to th e ca rbure tor. Compared to la st yea r' s Sn orkel design , th e ac tua l a ir in ta ke hole, which is now a ngled upwards, was m oved closer to th e steering stem whe re it is better protected by th e number pl ate. T h e a ngled-do wn posit ioning of th e intake hol e on last year's 406 ga ve flying di rt from th e AT K's o wn front wheel a nd roost from o the r bik es a stra ig h t shot into th e a irbo x. T uc ked n icely in side th e narrow engi ne cases is a five-speed gea rbox and a wet . m ulti-disc clu tch . ' Also found o n th e 406 is ATK 's p at ented C hai n T orque Elim ina tor design. The system removes excessive chai n to rq ue p laced o n the rear wheel when under hea vy ecceleration, whic h e liminates rear-e nd squat. T his reduces the work load on th e rear shock. The few inch es o f wh eel travel saved by the elim in ati on o f rea r wh eel sq ua t ca n ins tea d be used to absorb bumps a n d hol es o n th e tra il. T he o vera ll result is a smoother rid e. Another unique design on th e 406 is its rear d isc br ak e system. The di sc is m ounted to th e transmission 's co u n ters ha ft instead of o n th e rear wh eel. Its m ain advantages is less unsprung weight a t th e rear wh eel - five pounds to be exac t, according to ATK. But in th e past, ATK's co u tersh aft rear d isc brak e design wa s hampered by overhea tin g problems, resulting in prematurel y worn out pads. ATK. h ow ever. claim s this will no longer be a factor with th e 1990 models, after