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/126820
a n FZ750 spe c chart; the first time we relied on Bridgesto ne's speci fica tio ns for rear tire circumferen ce; we measured it th is time. We a lso fo un d d ifferen ces in valv e lift; Yamaha puts intake lift a t7.35mm a nd exha us t lift a t 7.2mm; we mea su red it a t 7.55m m and 7.l 5mm. And ca m timing, measured to a nd from Imm lift, seemed re ta rded fo r th e exhaust ca m, a lt ho ug h Yamaha was unabl e to p ro vide timin g specs with a measu ring point number; we measu red lobe centers for intake and exhaus t cam s a t 110° a n d 100.5°, respectively . Sueh iro Watanabe of Yosh imura R&D, wh o helped us with the cam tim in g and lift mea surements, figures tha t advanci ng the ' exh a ust cam tim ing from th e 39-18° we measured up to 50-7° (w h ich is close to th e in ta ke ca m's 7-47°) would dramatica lly increase available horsepower. Cha nging ign itio n tim ing to in , cr ease power p resents a p roblem , than ks to the Fl's unique ig ni tion sys tem. Sen sor s a re filled on eac h en d of the crankcases, o ne for each duallead coil. an d spark is triggered when a notch cut into the outboard flywheel on eac h side passes th e senso r. They can' t be adjusted . The carbs ca n't be easi ly cha nged, eithe r, since no a ftermarket, bolt-on downdraft carbs a re cu rre nt ly ava il· ' able. Beyond th at , th e FZ750's perfectly. fin e handl in g becomes a pro blem wh en th e bike is filled with slic ks and flun g arou nd a racetrack o ther th an Daytona, according to Fil ice, Dal e Qua rterley, J im Vreeke a nd ot hers tryin g to race Ya mahas in th e Superbike class. The problem s, a ll agree, seem to sta rt wit h the fro nt fo rks, which ha ve 39m m sta nc h io n tubes and ver y short, progressive springs with lo ts o f prelo ad . Fi lice a nd Valler ga tri ed CUlling off th e most -progressive en d of th e sp rings a nd adding spacers, increasi ng the vo lu me of oi l in th e legs, a nd ru n n ing 12 psi; all tha t hel ped, but didn 't cu re excessive .d ive. Fil ice sa id the forks arc genera lly too soft a nd that he co u ld feel th e forks bottom o ut enteri ng corners a n d th a t th e front wheel then skated to wa rd th e o u tside of th e track. Vallerga 's tal kin g abo u t changing the spri ng o n eac h damping-rod's highspeed co mpress ion. blow-off valve, designed to a llow the fo rks to react to bumps encountered un der brak ing; he thinks th e val ves o pe n too soo n a nd let the fork s com press too quickly. H e a lso th inks d ifferen t fork and shock spri ngs wo u ld help. But Fi li ce ci tes a lack o f reb ound dampin g a nd thinks a comp lete d ifferent set o f forks may be th e a ns wer. McDonald's Yamaha-backed Su perbi ke is filled with a T Z250 front end a nd still isn 't perfect. Wh ile a ll tha t's im portant to anybody serious a bo u t racing a modified FZ750 Yamaha , it doesn' t cha nge the facts rel ated to the stoc k, as-sold FZ . stree t bik e. It 's fa st. It 's q ui ck. It 's un comforta ble. It 's a n amaz ing motorcycle. Windage plates in the crankcases (above) keep sump oil from contacting the crankshaft: a baffle (be low, right) in the clutch cover does the same thing for the clutch. . For more about the Yamaha FZ750, see Cycle News October 3 . 19.84 (ba sic specificat ions and five-valve theory): Cycle News January 9, 1985 (developm ent ofthe FZ750 and detailed five-valve theory): and Cycle News March 20. 1985 (FZ7 5 0 vs . GSXR750 rid ing im pression). there's no extra charge for this service. And, K&K rates are competitive. Theres never been a better way to get insured. So what are you waiting for? Things aren't going to get any easier. WORKS UKE A SINGLE MOVING PARI