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/127698
R&D Racing Yamaha YZ125 _ _ _ _ _ _ _ _ _ _ _ _ y_D n MaedalPhoto s by Pau l Carr ut hers B.:.. _on T h e 'Ya m a h a YZ125 isn 't th e fastes t bike in the 125cc class, but th anks to its d ecent all-around m ot or, g rea t sus pensio n, good brakes and plea sant ergonomics, the testing staff of Cycle News p icked the little w hite ma chine as the winner of our ann ua l 125cc MX Shoot out. Everything about th e YZ w as appealing, and each and eve ry one of our test rid ers agreed that it w as the bes t-ro unded bik e in its class. At th e sa me tim e, however, we also agreed that w it h a little mo re in th e engi ne dep artment, the YZ would be the ultimate. Sure, it was fast enough stock, but everyo ne know s th a t at th e race track, a b one-st ock bike in th e 125cc class is a rarity . We could har d ly wai t to sta rt tw eaking on our litt le Yam ah a, and w hen we w ere given th e o kay, it was onl y a matter of d ays befo re we h ad bu ilt the bike we had dream ed of. R&D Racing is best-kn own fortheir wor k with the factory Suz uki m ini team in th e '70s and ' 80s, but remain o ne of Sou thern Ca liforni a's mo st popular hopu p shops. Th is year, the fathe r-a nd-son team of Rudy and Dean Dickinson have modified several motors for th e North (Above) Th ough it was alread y our fa vorite '95 125, we went on a mission to make the VZ12S even bett er. With the help of R&D Racing, Acerbls, N·Style, MMF and Afam,we bel ieve that we have bu ilt the " ultimate" vz. 56 County Yamaha Western Regional 125cc Supercross team, and it looks likely that they will be the tuners of choi ce for the tw o-m an squ ad . Th e Dick in son's we re m ore th an h appy to assist u s in o u r qu est for th e ul tim at e YZI25, and in a m atter of day s, ha d tr a nsf ormed o u r once mild-manner ed scooter into a real fire breather . R&D Racing ' s YZ12 5 engine kit is q uite extensive and - a t $553 - it isn' t cheap . Th is is w ha t yo u ge t fo r you r money: th e cylin der receives a radical port job that includes changes to th e deck he ight, as we ll as width and hei ght adjustments of th e intak e and exha ust ports. " It' s reall y a lot of g rind ing, " says Dean Dickinson, "very extensive." The cylind er h ead is - o f co u rse m odified to acco m mo d a te th e n ew cylinder deck height, and a t the same time worked on to increase co m p ressio n . The power va lves ar e also modified, and though Dickinson didn't care to elaborat e, he did sa y that the engine modifications included more than just a g rind here and th er e. Su rprisingly, the carburetor w a s left s to ck, w it h th e exception of a lea ne r needle-clip position . Th e final touch was the add ition of R&D ' s ra cin g ex ha ust pipe, w hich is speci fically designed to compli ment the afore mentio ned changes . The pipe is ch ro me p lat ed , w hich in add ition to adding a bit of style, m ak es up kee p a great deal sim pler. Ano the r su rprise is th e fact that R&D reco m mends the use of the stock silencer. "Aftermarke t sile ncers are so me times tricker-looking, bu t in m ost ca se s, th ey just make the bike louder," sai d Dickinson. R&D recommend ed that we run race gas, mixed with Ma xim a 927 at a 32:1 ratio. From the mom ent we sta rte d up the "bre athed on " m ot or, it w as a p pa re n t that the powerband was not of the same tame, a nyone-can-ride-it s tyle. Wh ile d yn o carts p rovid ed by R&D led us to ex pect .a " H o nd a -es q u e " p ow erband that begins with a hard hit down low that pulls strong through th e middle, th e Yamaha actu ally felt much different. 1 We had a stock '95 YZI25 on hand during testing, and jumped from bike to bike repeatedly . While th e stoc k bike see med to have a decent amount of low end and a healthy midrange, the bike felt a bit choked up on top. Not 'th at the bike wouldn't pull, it just felt as if there w as much more potential lurking in the cylind er . R&D h a s found a wa y to rel ea se that potential. Th ough the bike feels about the sa me down low, there is ab solutely no comparison from the middle of the powerband on up. The engine is a bit p ipier th an th e s to cker, but it rev s quicker and pulls longer . Our first rid e on the modified machine was on a watered sand track, and w e must admit th at w e weren't all that impressed. The ' torque- gobbling san d track mad e the R&D machine feel lazy in comparison to th e stocker, es pecia lly d own low. Our ne xt ride, howev er, came on the tacky, prepared surface of Rainbow MX Park. When traction w as abundant early in ) the day, the R&D engine scre ame d like a banshee. The more skilled th e tester, the better he liked the project bike. Even our beginner test er - whom we expected to • hate the bik e - found the R&D motor to hi s likin g, reporting that it hit harder' T and soone r. ' " As the day progressed and the tra ck • dried out, the R&D motor continued to amaze us . We thought that the harder - ~ hitting.motor would be a handful when th e going go t d ry and slip pery, but to our surp rise the bik e continued to hook up and ou tacce le rate th e s tocker. The R&D engine's only weakness is perhaps J