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/125837
The Yoshimura Z-l: If you always wanted a 96· hp street bike I always figured that Yvon DuHamel was faster than I am, but now I know for sure. Riding the Yoshimura-prepared Kawasaki 903 on which he won the Production race at Laguna Seca was aif revelation for me, because, despite:, the enormous power of "Pop" Yoshimura's engine, the thing is 'not easy to ride. Not for-me an:ywa¥. . Since we had a stock Kawasaki Z-1 to t~st, I thought it would be in teresting to get the Yoshimura Z-I, presently the most successful modified version of the reigning King of superbikes. Dale Alexander, who handles the stateside workings of the Yoshimura Racing operation, agreed to let me ride the bike. This particular motorcycle has quite a history. In one year it has set records at Daytona and Bonneville in addition to its Laguna Seca win. On Daytona's oval in March, with a special exbaust system, a fairing, and trick carbs, Yvon wicked the bike around to a closed course record' of 160.288 MPH. He also set a 10 kilometer record of 150.845 MPH and 100 KPH record of 141.439 MPH as well as a handful of other recor'as for various distances. A t Bonneville the bike wen t 162.842 MPH for a MPS-AS (partially streamlined, fuel). record. It set a Production mark in the trim that· we received it at 141.733 MPH. With full engine modifications (that is, carb and exhaust changed) but no fairing, it went 155.072 MPH. . Despite its illlpressive track record, the bike is still street legal. The lights and hom work and it still starts Yvon would have lapped the field. Our man c~,!ldn't catch the leaders. The bike was fast, but it takes more than honepower to win. electrically. The s~ds are gone, though: and steering -stops have been extended so that the bike will no lon~r make ,a. V-tum on a _narrow .,treet. Exhaust baffling is ·a· bit less. than standard (as large welding marks on the pipes testify), but it still isn't as noisy as some collector systems. The end baffles .arc..,still in ,pLa.ce. 'The pipes were cut at Bonneville and that alone added several MPH to the records. The Bonneville salt began to corrode quite a few pieces, so the frame was nickel plated before it began to rust. Except for the enormous Goodyear slick mounted on a special rim at the back, the paint job, and the absence of the tail section behind the seat, the bike appears to be pretty stock, which, if you're in to such things, can make for some entertainment when you arrive at a stoplight next to a competitive sort on another big-bore. The engine in the bike was not as radical as you might suppose. Displacement hadn't been increased and the lower end was stock. The modifications are the standard ones. The cylinder head has been reworked and fitted with differen t valves and valve springs. High compression pistons and a camshaft complete the Yoshimura modifications to 'the engine. The carbs are stock except for metering. The pieces are for sale out of the Yoshimura· catalog; your dealer can order them. They claim 96 horsepower. That's reasonable; it's broken a few dynamometers. The gear box on the bike is a recent addition. It is a special close-ratio set up that includes a tall first gear. The clutch in the bike showed signs of age, and it required gentleness when engaging it off ',,,the line. After that it was easy. The bike <;;:I\as l'ofs of punch at low end and it just . keeps coming as d'i~~.'s climb. We were -told to shift at ten ~nd,'but 9,500 was, 1where the thing see,!!~d to Like to shift. At that speed you were covenng-a lOt of . 'ground', even in first. First gear will get you a speeding ticket - on the freeway. Although it has ample power throughout the RPM range, there is a subtle power peak at about 8,500 RPM. The bike was geared for Bonneville, so we never found a place to use all of fifth gear, but it would indicate almost 140 - MPH' in fourth gear on the optimistic Z-I speedo. To find out a bit more about the performance of the bike, I took it to an ACA road race at Willow Springs. Willow migh t not have been the place for the bike. I think I would have felt more comfortable at Ontario - on the oval. But Willow gave me a chance to get some feel for comparative performance. It was the fastest street-legal bike on the track - by far. On one occasion I pulled up next to the 750 Kawasaki that I usually ride, one of the faster bikes in Continued on page 19 It looks stock, but 96 horsepower lurk within. It's street legal. Note the pipes. Photos by James Parker & Friedman 13