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 1B9B Yamaha YZ250 "cooperative" an d not -so-kind thi ngs like "laz y," "boring" or "hitless." Well, Yamaha was ou t to get rid of the latter labels - especially the "hit-less" part - by d igging into the mo tor and chan gin g it to coax more throt tle response from the . powerplan t as we ll as gi ve it a broad, usable an d potent spread of power. in their successful effort to gai n more power, Yama ha modified the com bus tion-chamber shape (head) and reduced the volume, u pped th e compression ratio slightly, and changed the position of th e spa r k plu g. The in take a n d exhaust port s w e re also cha nged in sha pe and match ed to th e m odified YPVS exha us t power valve better . The YPVS exha ust valve's fully closed positio n was a lte re d, and the go verno r asse m b ly was modified to make the va lve o pe n 200 rpm sooner than last yea r's bike. To e n h a nc e thro ttle response in extremely low-speed ranges, the pr imary gear-reduction ra tio has been changed from 2.818 to 3.0 by ad d ing a toot h to the prima ry drive gea r a nd removing one from the primary d riven gea r. Friction has also been reduced in the redesigned. w ate r pump, which now fea tures ba ll bea rings and a lumin um and steel internals rather than resin. The left-si de cra nksha ft and oil sea l have a new des ign to reduce friction. Also, the ig ni tion timing and the carbureto r set- tings were altered to work in conjunction with the cylind er and head mods. The mo tor mod s worked well because the YZ now barks with au thority. It's not a KX250 (which now sets the standa rd for thr ottle response and botto rn- to -mi d ra nge power ) in ab solu te thr ottle response or bott om-end power, but it' s pretty close and that's a good thing . It' s d efinitely gora "h it" to it. From there, ou r test rid ers felt the YZ had strong and long-pullin g power into the u p pe r rev s. It has m ore top-end power on tap an d more overrev than the KX, a lt ho ugh it's not qui te u p to par w it h th e king of top-end power, the C R250 . If th e KX250 h as almost to o much bott om end and Kawasaki is looking for top-end power, and the CR250 (Left ) The YZ250 Is much improved lor '98 and remains the same price it was last year: $5599. (Below) New port and Ignilion tim ing , a new eylinder head and modifications to the YPVS power-va lve system, among other thin gs, have given the YZ that "hit" Ya maha (an d customers ) have bee n sea rching for . By Cameron Coalney Pholos by Kil Palmer ~ r-, 0\ 0\ ...... r-...' ...... .... Q) ,.n E .... 0... Q) Q) CIl 14 ome thing strange happened in the world o f A me rican Supercross this yea r. Honda did no t win a single event and every o ther man ufacture r won at least a few, proving tha t Honda has not had some kind of secre t techn ology all these years other than four-time Supercross Champion Jeremy McGrath . Kawasaki won six rou nd s, Suzuki won three rounds and Yamaha won six rounds. The tide seems to have turned an d the factory-backed Yamaha YZ250 was definitely up to the challenge, and backed it up by also winning four ou t of the 13 National Motocrosses. In stock form, the 1997 YZ250 was a very willing and able motocrosser shod with a guod chassis and suspension package and an ul tra-smooth (and boring) motor. It was a bike that most people cou ld easily go fast on, wh ether they knew it or not. But it definit ely wasn't the fastest or most responsive bike out there. SO Ed Scheidler (the man responsible for the development of Americanbound YZS) and his team of testers and techno- heads dived into the YZ's motor in search of more throttle response and more power across the boa rd. He was also searching fo r better suspension action and any other improvements he could weasel out of the Japanese. After riding the bike for the past couple of weeks, we can tell you that Scheidler got what he wanted and the bike is awesome. The bike is so good, in fact , that if we were forced to pick a shootout winner right now, it would be the YZ. But it must be said that we have only had a limited amount of time on all the 250s - except for the Suzuki, which has yet to reach U.s . shores. The first thing Yamaha wa nted to do was make a motor the t had a "h it " image to il like th e other bikes ha ve. Their 250cc motor s ha ve been labeled kind thin gs like "smooth," "tractable" or