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/127193
found on most production motocrossers these days. Both Roeseler and Cunningham use cartridge forks on their KDXs. Roeseler uses 1989 . KX ca rtr idge forks, while Cunningham choses to run the 1987 KX fork with a cart ridge kit installed. Unfortun atel y, unl ess yo u jus t robbed a bank, you probably don't want to spe nd th e ex tra bu cks for a ccm p lete cartridge fork assembly. The much less expe nsive and effi cie nt Pro-Circuit-modified KDX fork cert ain ly does th e tri ck and sho u ld keep mo st enduro riders happy. It did for us . The ba ck end, which works fairl y 'well in stock conditio n , performs even better with th e P ro-Cir cuit mods. In stock form, the KDX has th e tenden cy to bounce aro und a little bit , especiall y ove r the sharper edged bumps, but th e modified KDX soa ks up th e jolts better. Over the ro llers, it is much improved with less hopping and uneasiness. H owever, we needed to bump up th e reb ound damping a little bit mor e and soften , the co m p ressio n just a tad because th e back end tended to kick a little bit too much when jumping over a ledge with a sharp lip. Otherwise, we were very impressed with th e new legs on th e KDX. Suzuki RMX2S0 O bvio usly, th e first thing most Suzuki owne rs are going to do to get more pow er out of th eir stoc k RMX is simp ly to remove a ll the restrictive and power-robbing a nti-noise devices that makes th e RMX EPA legal (82 db sou nd level ) for a trail bik e. But even with all the following modifications, our RMX is still quiet eno u g h to pass AMA's sound req u irem en ts "o f 98 db (w/spar k arr ester ) in off-roading events. To unchoke th e RMX you need to remove the airbox lid, the powervalve limiter, th e throttle slide stop, swap the abnormally thick head gasket for a thinner RM gasket, and it wouldn 't hurt to replace the heavy and very restrictive silencer with a lighter and less restrictive aftermarket muffler. At this point, the RMX IS defi- < nyone wh o follows th e motocro ss scene knows that Mit ch Payton 's Pro- Circuit R a cing has developed into one of the m o st highl y respected hi gh-performance aftermarket compa n ies in th e busin ess. Man y to p privateer motocrossers from all across th e cou ntry 'have come knocking on Payton's door in searc h of more power a nd suspe nsion tri ckery for th eir motorcycles, so th ey can be m ore com pe titive ag ainst the ~ factory race rs. Even some of today's factory MX bikes have had the ProCircuit magic wand waved over their mach ines, incl uding the entire factory 125cc Honda team. But mot ocross racing isn't ProCircu it's on ly forte anymore. Now th at the J apanese are showing more , and more inter est in off-road racing, Pro-Circuit is getting more involved in th e ac tion as well. Many of tod ay 's top o ff-ro ad stars are taking advantag e of Pro-Circuit 's wizardry. With thi s in mind, we handed ProCircuit two of th e hottest off-road motorcycles cu rr ently on the market - th e all -ne w Suzuki RMX250 and the totall y rev amped Kawasaki KDX200. Both m otorcycles are pl enty capa ble o f winning their class in sto ck form, but the modifi cat ions Pro-Circuit performed to th e Suzuki a nd Kaw asaki were designed for the more serio us off-road rider who want s ~ha t . ex tr a "ed g e o ver hi s co m peti to rs. Both m otorcycl es received motor treatment by Pro Circu it , while th e KDX als o had its suspens ion tuned up. Kawasaki KDX200 In stoc k for m, we liked th e KDX 's strong low- en d p u nch but didn ' t care too much ho w the power flattened out afte rwards . So Pro-Circuit gave our KDX the , same treatment th a t former four-time National Enduro Champion Terry Cunningham had performed to his Na tiona l Endurowinning KDX200. Pro-Ci rcui t touch ed u p a ll the , cylinder ports, lo wered the who le cylinder and head, a nd installed a new exhaust pipe, using the stock aluminum silencer/spark arrester. As far as carburetion goes , no jetting changes were needed. In stoc k co nd itio n, the ' KDX 's sus pens io n is ' 'adeq ua te but really isn't up to the job for A clas s enduro riders, so both front a nd rear su spensions received th e works. Up front, the stock non-cartridge Kayaba fork is set up out o f th e cra te too soft and too lightly dampened. Many KDX ' owners complain that the front end "pushes" in the turns. , To reduce sag, Pro-Circuit installed stiffer fork springs and modified the damping rods by increasing co mp ression and rebound damping a nd readjusting the external damping settings accordingly. Max ima 10 wt. fork oil is used and measured at the factory-recommended settings. The rear shock received th e' same treatment as Team Green's Larry Roeseler's KDX. Pro-Circuit uses the stock sp rin g but lengthens a n d revalves the shock. They make th e 'c o m p ressio n and rebound more sensitive for abrupt hits and more progressive for the bigger poundmgs, while the longer shock is to improve th e overa ll balance o f th e motor cycle, not to increase wheel tra vel. Roeseler feels the KDX rides a litt le low in th e ba ck. T he resu lts of Pro-Circuit's work is easily noticed on th e trail. Motor-wise, th e modified KDX feels lik e a sm allish 250 ra th er than a torquey 125 without the revs. Now it pulls hard from top to bottom ' without any lag in betw een , plus th ro ttle response is much quicker a nd snappier. Despi te gai ning more midrange and to p-end, we could n't notice a ny sacrifice in bottom-end punch . Our KDX now has a powerband you can .Ieel an d work with, and the in crease of horsepower is definitely noti ceable. You can a lso rev th e KDX a lot harder and lo nger wi th better results. The ' KDX a lso so u n ds more serio us with a throatier note. But to o u r s u r p r i se, th e KDX i s s ti ll extremely quiet, easily capable of passing AMA's 98-decibel sound level requirements for off -road ra cing. For closed-course racing only, you ca n install a KX silencer that doesn't have the spark arrester and gain a few more Rs. Suspension is much improved with th e Pro-Circuit mods. Overall feel is solid and stiffer, making the KDX more stable a nd predi ctable at higher speeds on rough ground. The fork soa ks up the jolts much better and you can plow through' the rocks and whoops with a lot more confidence than before. However, the modified fork doesn't feel as smooth or as predictable as cartridge forks