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/127930
PROJECT BIKE Power to the people: With its new motor and suspension mods , our project Honda XR400R has been transformed Into a sem i-se rious machine with racing capabilities. By Scott Rousseau 00 0\ 0\ ,...... 00 ,...... >-. . J-< Ie ;::l J-< ..0 &: 20 ss t! Hey, keep this quiet, but this mod ified Ho nda XR400R thinks it's a race bike. In s tock tr im, o u r middl eweig h t XR m ad e fo r a fu n little cow-trailer and , su r p ris in g ly, it even proved to be quite a kick in the pants at some of th e mot ocro ss parks that we frequent. The XR's nonthreatening pow er d eliv ery and ultra-cush suspenders flat made it a blast to playrid e in a variety of conditions. Th en w e mad e a mist ake w it h ou r joyous little thumper: We raced it. Th e ugliness occu rred at the classic Elsinor e Grand Prix, a high- speed, cobbly bugger of a place. Once we got up to spee d, we learned the true meaning of fear when the little XR revealed all of its girt h as it dive-bombed through its travel on any bump lar ger tha n a sandbag, bott omi ng both the front and rear ends with a horrendous clan k that sen t shivers - if not ou t and ou t shock load s - up and d own our spinal colu mn. Okay, so the bike was n' t that bad , but we ha ve to build it up a littl e, or else wh y read fu rthe r? Yet the truth of the matter is that we felt our XR could benefit grea tly fro m a few mods and that it cou ld be ma de into a raceabl e off-road motorcycle - you know, the kind tha t a vet or begi nni ng rider would enthus iastica lly th row a leg over for th e cas ual grand prix or enduro. First, we turned our atten tion to the suspension system, which we feel is an area wh e re a ny XR400R ow ner whether they be of an aggr essive nature, g rav ity -cha lleng ed, w h atever - cou ld ex pe rience so me ben efit by d epartin g from th e stock settin gs. So we phon ed our pals at Race Tech to give the XR's bum pers a once-ove r, Todd at Race Tech convinced us that part of the dilemma surrou ndi ng the XR had to d o with it s s p ri ng rat e s. The .39kg/ m m spr ing s up fron t a nd the 9.8kg/ mm in th e rear conspire to jack up the rear end, wh ich partially d ebilitates the for k by forcing it to d eal with to o mu ch forw ard w ei ght tr an sfer thr ough the bumps. The solution was to bee f up the legs by re pl a cin g th e .39 springs with a set of .43s so as to coun teract that d ive. We went even further by ac tually d ecr easing th e rear -sprin g rate, swi tching from the stock 9.8 spring to a lighter 9.2 in order to balan ce the machine's stance. In addition to the spri ng changes, the guys at Race Tech saw fit to tum us on to so m e of th eir bit chin ' s uspensio n products. A Race Tech Gold Valve compressio n-valve assembly was incorporated int o the forks . Basically, the Gold Valve is a high -p erfo r m a n ce v al ve assembly th at offers increased pe rfo rma nce an d tunablility, as the fork can now be revalved with standard shims, which Race Tech says are easier to wo rk wi th w hen making a cha nge. The fork was topped off with Race Tech 's own blend of US-2 10-weight fork oil. The s h oc k a lso re cei ved the Gold Valve treatment, the rear asse mbly featuring a 44mm o.d , valve that allows the pis to n to pass ' mo re oil. Race Tech owner and founder Paul Thede's take on increasing the flow is that it allows for increased plushness and be tter bump absorption while also retaining a g rea te r resist an ce to bottoming. Th e shock reserv oir, too, was filled with US2. All settings were tail ored per our request to sui t a l BO-pou nd Interm edi ate motocrosser. Motor m ods w ere nex t on the list, and it was here that we thou ght we'd use so me d iscretion. After all, we are well aware that there are seve ral companies that offer kits to turn the mild -mannered 400 int o a rip-sn ortin' beast. But pu shing the horsep ow er envelope also bears with it the risk of decreasing reliabilit y to th at of y ou r a verage h and grenad e. Besid es, we wa nted to ret ain the stock power cha racteris tics - we just wanted mor e power . Surprise, surp rise H ond a mak es jus t the thing th a t we we re loo king for. Design ed by Hond a Ra cing C orporation a n d extensively tested by Hond a's Baja /Off-Road racing team, the HRC XR400R Pow er-Up Kit is claimed to offer a IS-percen t horsepower inc rease over s tock th rough out the entire rev range, for controllabl e power. The kit incl udes a high er-compression pis ton assembly that nudges compressio n fro m 9.3:1 to 11.0:1; a high-performan ce ca ms h a ft th a t offe rs incre ased valve lift an d d uration; new primary drive gea rs that raise the gear ratio fro m 2.826:1 to 2.667:1; carburetor main and p ilot jets, and a ca rburetor needle; an outer clutch basket and heavier clu tch springs; a spark plug; an d a setup manual. The shop studs at American Honda performed the su rgery for us and d elivered the bike just in time for one of our day treks int o the Lucerne Valley. lt pro"ided the perfect op portunity to test the changes we ' d mad e in the face of th e new four-stroke benc hma rk, as we had both of the new Yama ha four-strokes along, too. The motor mods we re obvious rig ht from the time tha t we fired up the XR. The eng ine too k o n a s lig h tly more ra s p y timbre, and th e id le wa s a bit lu mpier tha n a stocker. On ce we started going through the gea rs, we did notice a conside rable change in the way the bike accelerated. Despi te a sligh t glitch in the carburetion righ t off idle, the increased torque and extra ponies were delightfully ap precia ble through the bottom and middle revs. Th ere di dn' t ap pea r to be any ou tstanding high -rpm performan ce, just a nicely execu ted increase througho u t th e ran g e, w h ic h a ll owe d u s to clu tch and s h if t the bike ju st a s w e would on a stocker. It was just more of th e same: more torqu e, more po w er , more fun. An even grea ter cha nge was felt in the suspension. The Race Tech hop- ups m ad e th e XR beh a ve mu ch better a t h igh s peeds . Plushn ess wa s greatly im p roved, as was the fo rk's abili ty to resist both bottoming and rebounding back too qu ickl y. We soon found ourselv es s la m ming into and over rock y o bs ta cles th a t w oul d have m ad e u s Outwardly, the modified components on the XR bear no clue to their "s leeper" status, but the HRC Power-Up kit and Race Tech-modified suspension are vast Improvements over stock.