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/141060
o < o ,- m 2 m ~ s: ~ Ul Karl Siega l h elped us out with the test . Th e b ike that is th e su bject o f ou r t est is Noguch i m odified ver sion of a new Y am ah a 12 5 c c m o t o cr osser avail able at this t ime in j apan. The bike is a production scaled d own version of its bigger brothers, th e DT3 and RT3 MX 's and represents a co m in g of age fo r the little moto cro sser in th at it now has very little. in co mmon wi th its end uro co u n te rpart. It is a co m pletely t rue production mo to crosser with its own special frame, engine and suspension. It is expected that th is bi ke witho u t any m ajor modifica tions will be introduced in this co u n try b y Yamaha at the b eginning o f the 19 74 m odel y ea r. T he p roduction AT5 MX , as it probably will b e cal led, will fe ature al l . th e neat goodies fo und o n it s bigger b ro th e rs. The engine is an all new design f e atu rin g CD1 ' ig ni tio n, To r q ue Induct ion a nd a t hro ugh the fra me rou ted ex pans io n c ha m be r . T he n ew frame ca rries the en gine lo wer fo r improved handling and n ow has m et al foldin g pegs fo r b etter foot grip. Fro n t fo r ks remain bas ically t he sam e as o n th e c u rren t 12 5 MX ex ce pt they have I " m ore travel . T he rear shoc ks are t he n ew thermal fl ow design wi th ex te rn al oil rese vo irs . Wheel rims are all oy with a 2 .7 5 x 21 Dunl ap a t the front and a 3 .50 x 18 h un g on the rear. Side panels, front number plate and fender s a re unbreakable pl as tic. What Noguch i did to o u r test b ike was m ake wh at will su rely prove to be a go od b ike eve n b etter. Becau se the eng ine is a production mill it co mes from Yamah a in a state o f tune that is re lat ively mi ld . T hi s is to insure reliability for th e average rid er a nd it makes the bike easi er to ride . No gu ch i insta lle d his sq ua re barrel cylinde r kit which raises th e p ower from th e stoc k (b u t p ipe y ) 22 bhp at 10 ,000 rpm to (a t o rquier) 30 bhp at8 ,8 0 0 rp m .The use o f a ch ro m e pl at ed alu m in um cy linder all ows the cy lin d er and piston t o ret ain the ir 'same int ernal clearan ces wh en the en gin e is runnin g an d has become hot. A hi ghl y tuned engine using a steel cy linder ca n 't ru n close cy lin de r to pist o n cle arances tha t are necessary for perfo rm a nce without ta ki ng the risk o f seizure due to the different expansio n rat es of st eel a nd alum in um wh en they a re hea ted . Also installed is a speci al expansio n chambe r tu ned to the new cy linde r and a No guc hi m odified Mikuni carb ureto r. . O th er Noguchi m o d ifica tio ns to the bi ke, o th er than t he e ngi ne , incl ud ed co m p le te m agn esium brake assemblies and a n alumi n u m works fuel ta nk. The b ike is pain t ed in Noguchi 's la test works team co lo rs: wh ite with a red center stri p e and a blue offset acce nt st ripe. ~ . David Townsley , owner o f Dirty Di s t ri but in g, gave u s t he Noguchi/Yamaha 12 5 t o t est .fo r a Saturday aft ernoon . Helpin g us o ut wi th the tes t wa s Karl Siegal, Dirty's 18 y ear o ld super speedste r wh o will be raci ng the bike in eas tern moto cross events during the up coming sea son. We wanted to te st the b ike in as close to Yamah a product ion spe cifi cat ions as possible in o rd er to get an im p ressio n of what the n ew Yamaha itsel f wo ul d b e like, bu t Karl had already gotten t o the bi ke and install ed his o wn han dl ebars an d a set of No guc h i fro nt forks. The Noguc h i fo rks are special lim it ed production it ems that Dirty wo n't be imp orting due t o th ei r expense , which is so m e whe re in the area of $3 00 .ea ch . Karl raced a No gu ch i 125 in the Florida Winte r-MIA Amateur seri es wh ich Was eq ui pped with stock Yamaha for ks that wo r ke d we ll, but afterwards he used a lat e r m odel b ik e with the Noguchi forks a nd liked t he m be tter. T he Noguchi forks worked sm oot he r an d we ren 't as harsh feeling as th e Yamaha forks. Th e d iffer e nce though isn 't w orth .$300. T he stock Yamah a fo rks could be rew o r ked to perform almost as we ll. T he bigges t exp ense on the Noguc hi fo rks are the s l i d er tub e s w h i c h a re s pe cial l ightwei ght cas tings tha t h ave been turned down o n a lath e. The alu mi nu m t ri p le c l a m p s ' a r e precisi on hand machined fr om alu m in u m and th e p in ch bolts are titanium . F o r su ch a highl y tu ne d raci ng m achine t he 12 5 is easy to start. just flip d own the enri cheni ng lever on t he specia l 2 8mm Nogu chi m odified Mik uni carb u re t o r, give it a little throttle, kick the starter lever once or twi c e and it 's running. It should be po inted out that th e new Yamah a's along with having a new engine, has a new kick start lever assem b ly wh ich fo lds co m p le tely out of the wa y wh en n ot in use. No more a n kle b anging. The kitted engine id les smoo thly without a hint o f trying to load up. Hu m , I thought t o m yself, this ca n 't really b e a rac ing bik e. Well, th e bes t way t o find ou t is to rid e i t so I clic k t he shift lever do wn into first gear, rea lly rev t he engine and le t o u t o n t he cl u t ch gingerly. I wasn 't read y for what happe ned ne xt. 1 was expecting either a tire smo king wh eel ie or fo r the e ngine t o jum p a nd di e. It did neither b u t just pulled away smoo t h ly as 1 fou nd I co ul d ju st le t back o n t he th rottle an d st ill get u nde rway easi ly . Ge e, th is is sure a lot easier than 1 thought it would be. But wa it! Wic kin g on the th rottle brough t an instant su rge o f p ower t ha t started the tire sp inn ing a nd m e slid ing b ac k o n th e scat. Bette r sh ift t o seco nd qu ick . Zap th e th ro ttle. Shift, za p . shift , za p , shift an d zap agai n . Gawd t hi s thing is fast! As fas t as m y 250 motocrosser .. well almos t anyway. But it sure is smoo t h . The p ower is al most ro cket like. just cra n k it o n an d it goes . There is no .. aiting for th e revs to build up v an d get the e ngin e o n the p owerband b ecau se if yo u 're in the right gear th e engine will pull with out hesitati on . The bike is honestly easier to ride th an the present stock Yamaha AT3 MX an d t he Noguc hi has alm o st 40% more power . It actually is t o rquier feeli ng too. Karl 's impression when he firs t ro de t he bike was tha t it was strong er, but th at it was also mu ch sm o other than hi s o ld bik e. Ad di ng to the smoot hne ss o f the power is the e ngi ne itsel f wh ic h is to t ally ru bber m oun ted in the fram e. The re is no vib ration whatsoever whi ch a t first impression reall y amazes you. We had a ch anc e t o loo k at one of th e No guchi cylin d ers . Whil e th e porting lay out lo oked fairl y similar t o wh at is stock o n th e Yamaha mot o cro ss. the Noguchi cy lind er d o es not h ave the auxiliary transfer p ort co ming up from th e intake p assage. Noguc hi sa ys this fi ft h t rans fer p ort is just a gim m ic k an d isn't necessary o n the Yamaha reed indu ct ion syst em. This seem s rath er difficult t o believe .whe n so m an y s ucc e s s f u l r eed a p p l ica t i o n s use aux iliary trans fer ports cut up into the co mbustion chamber from the int ake p assage. The No gu ch i cy linde r d oe s work t houg h , an d quit e well, so we 'll have t o beli eve h im . After all, Noguchi is the Yamah a fac t o ry raci ng team manager and one of their main de vel opment en gineers , besides being the _most respected tw o stro ke engi neer in j apan. Ok, so t he engine is good . There is no need t o go o n a nd say an ything abou t th e Yam ah a t ransmi ssion , clutch o r s hifter b e c aus e th e y'v e a l r e a d y establis he d th emselves as amon g th e b e s t a va ila b le an d a re c l ose to i n d e s t r u c t a b l e . T he A utolube o il injec tio n system does not co me on the AT5 l\IX. For an enduro o r stree t bike th e Autolube is the way t o go, but it d oesn 't belong on a 100% racer. But how d oes it handle? In o n e w ord . beauti ful. exc ep t fo r th e stoc k rear shocks. Dam p ening act ion in the ne w shocks felt a ll right b ut the springs wer e too stiff for all o f us who rode the bike. Rep lacing the m with 70 pou nd o r 60/90 pound p rogressive springs should so lve th e prob lem we had with t he rear en d bou nc ing. The new fr a me makes th e AT5 MX the best handling Yamah a motocrosser yet. Eve n better th an th eir 250/360 series 3 MX 's becaus e the AT is so much lighter. The Noguchi m odifications have trim med off ab o ut 20 pounds fr om the production m odel , bringing th e weight down to 180 p ounds. S till, the bike in st oc k co nd iti o n will be a super handler. Wheel base has been in creased from 50 to 53 in ches . The new fr ame moves the engine fu rthe r fo rwa rd a nd lo we r to the ground, but st ill m an ages a good 10 in ch e s o f g roun d cl earance. The crankshaft ce nter of the engine lies o n th a t th eoriticall y d esir abl e lin e whi ch runs fro m th e fro nt to rear ax les with th e c ra n k being eq uid istan t from the tw o p oints. This m akes th e bike a very predict abl e an d smoo t h handler. Getting it o ut of shape reall y ta kes a lot of effort, b ut if you d o , it wan ts to st raigh te n itself rig ht up. With as m uc h po we r as th e No guch i e ngine d evel op es th e bes t m eth od fo r ge t ting aroun d a track q ui ckl y is to sq uare th e co rners . The exc ellen t brakes le n d th emselv es to this st y le quite well , especially th e rea r o ne wh ich is now a full flo at er. T he Noguchi/Ya maha will slide easily bu t powe r on with th e bike laid over causes t o o much wh eel sp in and th at means wast ed time in a tum. When t he bike is upright it can get its best traction, so with a b ike that stops and acc elerates this well. squaring a turn is the o nl y way . W e fell in l ov e w i t h the Noguch i/Y amaha 125' m otocrosser, It is not as highly strung a bik e as we first th ought it would be, meaning that it can be ridden easily by an expe rie nc ed ri der, but un like m o st other 125 's there is so mu ch waiting in res erve that o nly a re all y go od rid er will b e able to reach hi s p otential o n it . It looks like Yamaha will have a winner when they rel ease the new AT5 MX . It is a real handler, but as we said before, it won 't be much faster than th e p resen t m odel. However , the p ip ier power b and on the AT5 MX sho uld m a ke it harder to rid e than the present m o d els. Mo st riders will probably find it has all the po wer th ey ca n use, but if you ca n hand le m o re the Noguch i set up is the way to go a nd it sh o uld p rove even easier to co ntro l. For tho se of y o u wh o already own Ya maha 125 MX 's th e new Noguchi sq ua re barrel ki ts will bolt righ t o n to you r p resent en gin e, and then later o n if you get a new AT5 MX the sa me kit ca n be installed on it. If yo u can ' t wai t un til ne x t fall fo r a bike, Dir ty Dist ributing is presently b ringing ov e r fro m j apan a limited num be r of the Noguchi m odified 12 5 's fo r sale at S 1095. If you wa n t the fas tes t a nd one o f the bes t handl ing 125 's on th e block, this is it.