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/127805
.RI.DING IMPRESSION 1997 Yamaha YZ250 slowly. Basically, the motor felt lazy. Well, don't fret anymore, loyal Yamaha motoheads, for 1997 the YZ250 motor is back and better than ever. Even without a longer rod. The heart of the changes in the 1997 Yamaha YZ250 motor come in the form of a revised cylinder. The port timing and exhaust port shape were changed and longer intake and exhaust ports .were designed. The intake port is now 7mm longer and the exhaust port is a whopping 15.5mm longer than the '96 modeL The combustion chamber in the cylinder head was changed in confi~ ration and now has a volume of 23.1cm3 over 22.lcm 3 in '96. The scavenging ports in the crankcase. also were changed in shape. The reed-valve went from a six-petal to a four-petal design and the exhaust pipe was redesigned to work in conjunction with the new cylinder porting, and intake and exhaust configurations, especially at higher rpm. The COl received new timing characteristics to work with the 'new cylinder and exhaust designs. All of these changes were directed toward creating more overall power and for greater throttle response in ail rpm ranges, last year's major complaints. To help get this new-found power to the ground more effectively, the clutchdog shape in the transmission went to a straight taper rather than the reverse taper that was found in the '96 transmission to smooth out gear changes. The clutch was updated with the addition of a bearing and washer between the pressure plate and the pushrod for easier operation. The changes didn't stop with the motor, either. The chassis was changed wi th a very small reduction in rake angle to aid in quicker cornedng. But don't worry, it wasn't enough to nullify Yamaha's traditional stability. To increase overall rigidity and durability, the wall tubing thickness in the frame was increased and the frame got a stronger gusset under the head tube. The front motor-mount bolt was increased from 8mm to 1Omm. In the suspension department, the front forks went to a non-recirculating design, which is what all of the factory guys and aftermarket companies have been using this last season. New valving and stiffer springs (from .42 kg/mm to .43 kg/mm) were installed to improve the fork action for riders of all abilities. Out back, the shock gqt new valving and a heavier spring (from 5.2 kg/mm By Cameron Coatney Photos by Kit Palmer '" 0\ 0\ T'""'i ",'" T'""'i l-< OJ ~ o 38 ooking back, the 1995 Yamaha YZ250 had a smooth, yet fast, always-hooking-up kind of motor that was universally praised by the motocross community for its ability to produce a very controllable spread of power and thus, faster lap times, especially with the installation of Yamaha's long rod kit that just spread the powerband out even more. So for 1996, everyone assumed (and prayed) that the YZ250 would come stock with the longrod kit or a comparable cylinder. This was not the case. The 1996 YZ250 motor produc~d good, usable bottom and midrange power, but it didn't have a whole lot of top-end power and it buil t rpm very (Above) The 1997 Yamaha VZ250 stili crsves and excels In dry. hard-pack conditions but hes better throttle response and topend power ihls yeer. (Right) Yamaha Jumped right back into the 1997 VZ250 after last year's maJor overhaul, giving tha blka "team" colors and graphics and the motor a muchneeded boost In performance.