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/127209
Racer Test: Bimota YB4EIR Superbike A four·stroke GP bike by any other name By Ala n Cathcart Photos by Phil Masters l] ere.s no 'contest for the unofficial Rookie of the Year title in 1989 World Championship Super- 10 bike roa d racin g . In o n ly h is seco nd full season of roa d raci ng a t a ny level . form er mot ocrosser Gi ancarlo Falap p a of It al y h a s co me from nowhere to amaze hi s riva ls with hi s speed and determina tio n. th rill the crowds with his biza rre-but daredevil riding style. a nd vindicate Bimot a boss Giuseppe Mo rri fo r having chosen h im to lead the small Ita lia n factory's attack o n the Worl d Superb ike ti tle they so narrow ly fai led to -w in last season. By repl acing Birnota 's long-time, . number- one rid er , Italian Davide T a rdozzi, Fa la p pa's a rriva l sym bo lized th e start o f a new era for Bim ot a - a fact given even gr eater em p hasis by th e departure o f th e company's ch ief desi gn er , Frederi co Martini, to G ilera in Mar ch this year. Given that Ma rtini , ge ne ra lly accredited as th e arch itect o f Birnota 's rem arkable rise from th e as hes of bankruptcy to th e status o f a cu lt marque in th e past five years , was a lso th e desi gner o f th e YB4EIR S upe rbi ke racer, th e pund its wer e ready to write off Bimota's cha nces of success in th e " '89 Superbi ke World Seri es - especi ally as th e homologati on rules required th em to co n tin ue racing with the half-a-decade-old Yamaha FZ750 motor fitted to th e YB4 stree t bike, rather than th e new , ultrashort -stroke FZR engine em p loyed in th e OWOL . T ha t mi ght have been the case, but for a nu mber of factors. First, Birn ota 's version of th e. FZ750 engi ne has become a pretty reliable piece of tackl e. whi ch the 0 \\'01 most definite ly is no t' (ye t) . Tw o, a ft e r development problems with the innovative Weber/ Marelli EFIIE MS a lmos t certai nly cost the " B-BBirnotas" the ina ugura l Superbi ke ti tle last season, this has now been refi ned in to a depen dabl e syste m wh ich g ives th e team a n undo ubted edge in sett ing up the bike, as well as extrac ting perform an ce from th e obso lescen t eng ine. An d last, bu t definitel y not lea st, Martini 's successo r, developmen t enginee r Pi er luigi Ma rconi, th e youthful crea to r o f th e revolutionary Tes i of a Iew years past - a nd th e factory's race engi neer fo r th e past co uple o f seaso ns, was both o bvio us a nd accom p lis hed. U n der Ma rcon i ' s di rect ion , Bim ot a has tak en .th e YB4 des ig n, wh ich debuted in 1986, won th e World TT Formula One title in ca rb ure ted form in '87, nearly won th e Su pe rbike cro wn in its first yea r with EF IIEMS in '88, a nd at th e time o f writing ha s won three of th e 10 races ru n to dat e in this year's World Supe rbi ke Seri es, to its ultimat e level o f develo pmen t. " We're a t th e lim it o f o u r potential with th is engine, " says Marconi with a fata listic sh rug. " T he re's no more to come. And since we ca n't use th e OWOI engi ne .in o ur bike, and have no plans to ho m ol ogate it by using it in a road bike, th is is as far as we ca n go in Su perb ike raci ng at present. " He nce Birnot a 's pl ans to go G rand P rix racing wit h a n a va n t-g a rde 500cc twi n in 1990 - th ou gh if th eir p resent in ten t co mes to fruition , th ey'll be back in Superbike racing with a n ex treme ly exci ting, nonj apanesc-en gined b ike in 1991. Well, figure it o u t for yourself . .. In th e meantime, therefore, Fa lappa's brace o f works YB4EIRs th a t I , sam p led d u ring th e factory's midseaso n test sess io n a t Rij eka in Yugoslavia represent a tri umph of empi rica l developmen t. Wh en I last rode a works YB4 - Tardozzi's TT l bik e fitted with 34m m Mikuni ca rbs - a lmos t three yea rs ago to th e day of my Yugo outing, the en g ine delivered 115 bhp at 12,000 rpm, with tuning parts mostly restricted to the co n ten ts of th e Yamaha FZ750 race kit. The sa me ba sic en g ine ha s now been persuaded to deliver no less than 132 bhp a t th e rear wh eel at 12,200 rpm. This is in race form , th ough on th e d yno Marconi has seen 137 bhp, but with a n unaccepta bly narro w pow erb and. However, to ac h ieve this Bim ota h a s effec tively re-en g in eer ed the motor so th at o n ly the Yama ha o uter casti ngs rema in. Cranksha ft, conrods, p istons, valves, springs, earnsha fts a nd cylinde r sleeves have all been specia lly made to Birn ot a 's specifica tio n by a variety of Eu ro pean co mpone n t su p p liers , wh ile Yam aha su p p lied sp ecial versions of th eir clo se-ratio FZ kit gearbox to Birnot a, with sho rte r ratios in eac h of th e bottom th ree gears of the sixspeed box. Four of th e team's five ra ce engines use Yamaha's dry cl ut ch , but for some reason th e fifth m otor wa s supplied with a standard oil-ba th clutch which ha s proven invaluable. Apparently, th e Yamaha dr y clutch ha s no exha ust for th e dust off th e plates, which means it tends to slip