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/126902
The Yamaha YZ has slightly less horsepower than before but suspension is vastly improved. The YZ does everything well. terrain tires. The 1985 disc brake and plastic brake hose is used up front. The all-new motor received more than just a color change for 1986. Suzuki has joined the power valve wars with its new design, similar to last year's Honda ATAC system which automatically adjusts exhaust resonance by using a valve and an exhaust sub-chamber. At low rpm, the valve is wide open, letting exhaust enter the sub-chamber. In theory, this increase in chamber volume reduces back pressure and increases low end. s rpm climbs, the valve begins to ose, reducing chamber volume and ncreasing back pressure to maintain ower on top. On the power valve nit, there's an adjustment knob to Iter when the val ve opens and closes, 1I0wing tuning for different track onditions and rider's preference. The Suzuki has a case-reed inducion system, a lighter connectin~ rod (8.28 to 8.18 oz.), a center-port exhaust pipe with a new oval aluminum silencer, and a redesigned water pump system. The water pump is now driven directly off the crackshaft and pumps coolant directly to the cylinder head, eliminating two hoses. The radiator has a double-core and larger water jackets for better cooling. To help improve low-end performance, Suzuki went back to a 36mm flat-slide Mikuni carburetor, from 1985's 38mm. The airbox assembly is all new to fit the new frame and rear suspension. Access to the filter element is now from the top (instead of the side) after removing the seat, and the whole unit is larger than before. The five-speed transmission received the once-over and has slightly different ratios. The totally rebuilt clutch uses a rack-and-pinion set-up to make the engine slimmer and to The Suzuki RM needs a·lot of fine tuning right out of the crate. Motor is slightly better but still lacks bottom-end zap. maintain consistent action when hot; Suzuki trashed the push-rod design previously used. . Honda CR250R Last year, the Honda CR lost its stranglehold in the 250cc class due to a weak motor and poor suspension. So it's not surprising to see an allnew motor and refined suspension on the latest CR250R. Honda went straight to the powervalve in search of more power and chucked the ATAC design for a totally new system, called Honda Power Port, or HPP. Unlike the ATAC system, which changes exhaust volume according to rpm, the HPP design has a rectangular valve on each exhaust port; the valve changes the size of the ports according to rpm. Atlow rpm, the valve closes, reducing port size; at high rpm, it opens, increasing port size. Although the HPP design seems efficient, it is mechanically complicated, and requires constant maintenance. The valves are susceptible to carbon build-up, which can make the valves stick open. Honda recommends using top-grade oil and tearing down the top end after every two hours of riding to inspect the valves and remove carbon. One Honda spokesman's explanation of'this ritual is "Si,nce the public wants workslike motorcycles, they'll have to accept Suspension: hese two charts show how the 250s perform and compare to one nother in nine different categories. Colors indicate each motorcycle: ellow. Suzuki; red. Honda; green. Kawasaki; blue. Yamaha. Fair Good ~ Exc. Motor: Poor Fair Exc. Good Cll .E :a c :• z: ~ II :t 0 Q, Cll C ~ • ~ ID l E555555555::~ • 1:: ... E 0 0 () 15