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/127857
RIDING IMPRESSION 1998 Kawasaki KX250 By Cameron Coatney Ph otos by Kinney Jones I,l Il \]JI.1 he ther you want to admi t it or no t, the Kawasaki KX250 has been the dominant motorcycle " in professiona l motocross and supercross competition for the pas t coup le of years. In the hands of the ma tu red Jeff Emig , th e KX250 has wo n th e 1996 Wo rld Supe rcross Champ io ns hi p , th e 1996 AMA 250cc Na tional Motocross Championship, the 1997 AMA 250cc Supercross Cha mp ionship and, most recently, the 1997 250cc National Motocross title. Yes, the bike is evidently good in Jeff Emig 's po ss ession , but w ha t makes things even more impre ssive was how well the bike worked in the hand s of the Everym an - you and I. The bike has been really good the past couple of yea rs for the average Joe and could have won our 1997 250cc shoo t-ou t had we not been oo h' ed and ah' ed so mu ch by the alumin um wonder last yea r. Its excellent bottom-to-midrange-tailored power and incredibl e throttle response - wit h suspen sion to back it up . mad e it the easiest bike to go fast on for almost every one of our testers. So did Kawasaki ma ke the 1998 KX250 any better? Could it even be don e? It could and they did . You probab ly w ouldn't think th at Kawasaki would mess with a good thing - the KX250 motor. But they did , and the resul ts are excellent. While sitting in the pits of a local race a t th e end of '1996, Kaw a saki of Japan ' s Jeff Matiasevi ch mentioned the "big valve" that his works bike ha d tha t w ou ld be comi ng to the production bikes someday soon. He said the power was incredible. Well, the "big valve" is here in the all-new cylinder that Kawas aki produced for the KX250, featuring a wider main exhaust port (from 44 to 48mm) and smaller exhaust sub- . ports for mo re efficient KIPS (Kawasaki Integrated Power Valve System ) operation. The center KIPS valve is now wi der (41 to 43mm ) for better exhaust-port contro l and sm aller KIPS rot a li ng drum valves (21 to 17mm) work in conjunction with the new exhaust su b-ports to search ou t more power throughout the range. While they we re at it, the KIPS governor spacers were thickened for increased d urability, and the p iston-ring-gro ove tolerances were tightened up. The bottom end received some atten- 12 tion as well, ge tting a new cra nkshaft wi th the mass concentrated closer to the center of th e. sha ft to off set the m u ch smaller flywh eel used for less vibrat ion, smoother o verrev and lo ng er-lastin g main bearings . The crankpin holes were th en plugged , crea ting mor e primary co mpress io n, a nd the co nnec ting rod now has two oil holes (instead of one), bigger oil grooves and chamfered washers at the big end for improved lubri cation and du rability. The crankcase was also reinforced ne ar the cen ter engine mount for more engine rigidi ty. Follow ing Honda' s lead , Kawasaki us ed a Keihin Power Je t PWK 38mm car bure tor on the KX250 that still features the air-velocity wings on the airbox side of the venturi and a crescen tshap ed slid e. Like the power -je t carb (Above)The 1998 Kawasaki KX250 has been Improved and should be hard to beat on the track. Just ask Jeff Emlg. (Be low) In order to boost last year 's awesome throttle response and bottom-to-midrange power . as well as give the bike better top-end power and overrev , Kawasak i designed a new cylinder. KIPS system , and crank and added a Keih in Power Jet carboThe results are ~tunn ing. that also comes standa rd on the KX125 in ' 98, the KX250 power jet is locat ed much further down in the carbureto r than Hond a's vers ion . -Kawasaki claim s tha t this gi ves the bik es be tter po w er throug hout the re v range , s inc e the power jet starts releasing fuel sooner as th e slid e op en s an d the ventu ri e ffect - starts pulling fuel into the cylinder. The power jet stays open on the KX250 until an elec tro nic solenoid closes the fuel passa gew a y at 8100 rp m, effec tivel y leaning out the fuel mixture by 10 percent for be tter top-end power and ov errev . A longer pro tective tube has been added to the throt tle cab le, whi ch also has a Sm m- Io ng e r inn e r ca ble for improved durability. . Change s to the motor continue with th e .6mm-Ion ger reed s that also ha ve 1mm more lift, as well as being made of a new material, in search of better throttle response and more top-end pow er. The ignition ' timing wa s also cha nged , and the igniter, which has been relocat ed from the head tube to the airbo x, is pro-