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/126891
Push-pull throttle is from a Honda CM400; push-pull throttle relieves - spring-pressure with stock throttle and Keihin CRs. the Ninja's stock constant-vacuum carburetors, cranking the throttle wide open atlow rpm will cause the engi ne to yawn, cough and stumble. . The big improvement in perfOTma nce comes in the 5000 - 8000 rpm range. Though the extra midrange punch wasn't re(lected in the quartermile times, the difference IS' unmJStakable. Where the stock Ninja feels peaky, and wants to be kept at the top of its powerband, the Keihin CR Specials make that powerband considerably broader, eliminating much of the footwork with the Ninja's sixspeed gearbox. Ho"wever, since velocily stacks are not conducive to long engine life, the Attack Ninja was fitted with a set of K&N air filters to replace the stacks. The left-center filter was inverted to clear the crankcase breather hose of the Performance Works oil catch tank. h's a tight fit, but the Keihin CRs with four K&N filters will just clear the Ninja's sidecovers. As would be expected, the jetting had to be changed to accommodate the air filters. After some experimentation, the Attack Ninja seemed happiest with a YY8 needle set to the third clip-step (from the bollom), a #250 main air jet, and the same #120 mai n jet. No adjustments were necessary for the air screws; once dialed-in, velocity stacks can be filled in place of the K&N filters in less than 10 minutes. Because theCR's big 33mm bore passes so much air, it:s easiesLto start the engine when the idle speed is set below 1200 rpm. A side benefit to the Performance Works kit is the removal of the emissions hardware; and getting rid of all those hoses and fittings considerably improves engine access for routine maintenance. The kit enables the removal of the stock air-injection manifolds, reed val ves, the air switch valve, the liquid/vapor separator, the charcoal canister and about 20 feet(!) of neoprene hose. Not only is the bike more reliable and easier to work on, gone forever are the worries of gasoline plugging the accursed charcoal canister. Though the Keihin CR Specials are claimed to work with the Ninja's single throttle cable, e~perience showed that on occasion the slides would momentarily hang open: a result of manifold vacuum when the throttle was closed. To combat this tendency, the bank of carburetors is fitted with a strong return spring which translates into much greater effoTlto hold the throttle open. However, in spiteof Keihin's macho return spring, the CRs would still hang open with frightening regularity. Fortunatery, the Keihin CR Specials are fitted with the linkage for a push-pull throllie. For the Allack. Ninja, a suitable push-pull throllie was transplanted from a crashed Honda CM400; the exact model and year aren't important: a local cycle_ salvage yard should be able to supply a similar used throttle housing, switch cluster, cables and wirinR harness for (Continued to page 54) 37