Cycle News - Archive Issues - 1990's

racer that RPM b"uilt for us is that the ove r-3D crowd at Cycle News wou nd u p being too busy wit h the wives and kids to even ride the finis hed product. Therefore, th e project was h a n d ed ove r to younger test ers and one Vet Pro racer by the name of Craig Davis, who ' used the bike to smoke most of the Vet Pro races in Sou the rn Californ ia in the few mont hs following the bike's com pletio n. Teamed with Peterson, Too Tech Suspension' s Rick John son , a nd Davis, we came to th e realiza tion th at w ha t wo rked for Davis d id not wo rk for ou r slowe r testers . . The beauty of the RPM YZ300 is that it can be buil t to sui t all styles . By using d ifferen t th ickness base gaskets and different FMF p ipe s a n d s ile n ce rs, th e power characte r is ti cs can pract ically mak e the b ik e an ything fro m a road ra cer to a tra ctor. We test ed the bike with th e FMF Po w ercore II s ho rty silence r, and naturally it increased low end at the expense of over-rev. To try so me thing d ifferent, w e bolted on an FMF Tur bine Core II spark arrestor and the bottom end d ecre ased , while peak powe r and over-rev increased . Davi s prefers a thin base gasket .with the short silencer becau se he is capable of handling the bike' s brutish acceleration out of corne rs. He was able to gain What's a rocket-fast motorcycle without a good su spension setup? Too Tech dialed up a great suspension package, allowing us to ride the YZ300 to its full potential. ge t-o ff. All of th e minor changes tha t our bike underwen t proved how versa tile th e engine is and how crucial th e setup can be on an RPM-built motor. . Once ou r ow n p ow er tastes w ere so rte d ou t, our a tten tio n was turned toward the suspen sion. At th e sta rt of the project, Peterson had hooked us up wi th Rick Johnson of Too Tech Racin g. No stock sus pe nsion is perfect, so th e two Ricks spent a couple of days with us at Glen Helen Raceway Park, dialing in th e leg s of our new mo ns te r Yama ha . First a nd for emost, Joh nson d oes not believe tha t cha nges to the stock shock or fork internal pis tons are requ ired to achieve goo d sus pe ns ion performan ce. Mod ern OEM in ternal piston feed circuits offer good con tro l and genera lly ade quate flow . Johnson's theor y is that the stoc k rear sus pension on a '99 YZ250 need s less low-speed d a mp ing so it is less likely to ride high , forcing weigh t to the front. Faster riders actua lly need less h igh-speed d amping so the sho ck can' blow th rough the squ are edges at fifthge ar sp eed s. To correct th e probl em, Johnson installed a heavy-duty bottom ing bumper to complime n t the valvin g changes. Johnson also believes that the fork is actua lly over-damped for sha rp bu mps. He mad e cha ng es to the midspeed valve, causing it to op erate wit h less spike while ad ding bottoming resistance . Th e low -s p eed s ta ck wa s a ls o ad justed to opera te less abru ptly. Obvious ly, afte r makin g the internal cha nges, Johnson a lso conce ntra ted on the sp rings. As expec ted, Da vis op ted for stiffer s p rings. Johnson ins ta lled a 5.2 kg / mm shock s p ring fo r th e 165pound Davis. Th e fork go t a .44 kg / mm fro nt spring wit h an oil level of 3.5.inches. That se tup was too stiff for ou r riders, but it wo rke d ex tre me ly well fo r Davis. Because our tes ters cou ld not get comfo rtable on Davis ' settings, Joh nson went back to the drawing board , someth ing he w ill d o fo r all his cus to me rs u ntil thei r suspension setup is to their liking . A 4.8 kg/mm shock sp ring replaced Da vis' heavier sp ring . The fork stayed the same with the exception of less oil. Instead of Davis ' level of 3.5 inches from the top of the tu bes r3.75 inches from the top was more to ou r liking. With th e slower an d lighter settings we were able to ge t aro u nd th e tr a ck fa ste r for a longer period of time. The harshness on b raking bumps a nd the ten d en cy fo r head sh ak e d isappeared. Johnson' s Too Tech Susp ension settings cleaned up the somew ha t stock , rigid feel, but still left ou r YZ300 w ith th e ab ility to land th e har d est land in gs w ith confid ence th at we weren't going to pogo off the track. At the same time, we weren't bottoming out either, jus t doing lap af ter lap on a we ll-balanced motor cycle. The mor e time we spent on the RPM YZ300, th e mo re w e w an ted to tink er with it, turning it into a fu ll-blown offro ad ra cer or even the Super Mo ta rd Cap omo bike that we bro ught up ea rlier. With Pe terson ' s m ot or w ork a nd john son ' s sus pe ns ion kno w led ge, there is no d ou bt in our mi n ds that the tw o ca n bu il d a ny kind o f co m peti tio n motor cycle d esired. The bottom line is, if you wa nt to grab mon ster holes hot s a n d p odium fin ish es, RPM a n d Too Tech can h elp . Bu t yo u'd bette r ca ll eN them before your buddy d oes. . A dy no chart speaks a thousand words. Well , t hat, and this picture (left) of Craig Davis blasting t hroug h a deep sandy berm . ma ny- ho les ho ts w ith th at same se tu p, starting in third gea r on cement starting pad s. Davis even scrapped the stock SOtooth rear sp rocket for a 49 to increase th e pu ll bet w een gears . Under Da vis' command, the YZ300 felt like an ope nclass bike that dema nd ed attentiveness . Our m ortal te s ters le a n ed mo re towar d the stock base gas ke t, stock gearing and FMF spark arres to r. With thi s se tu p the YZ300' s pow er d elivery felt mo re like th a t of a fac to ry 250cc machine. The bike cou ld still be ridd en a gea r higher in most p laces, but minor mistakes with the throttle were less likely to resu lt in an unplanned wheelie or - - Cyd_ NflwsVZ300 ~ • • • .. . Stock 99 VZ250 29

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