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/126515
'full-on ~..... I~low. left to right) SIde coven ere 8fterm"utt Item•• IpIIot pouch. Kliyebe MocQ enclentl-dlve fork. . . "nckieJlWd exam'" of Yoshimura's Daytona· · 5 · .:U-- By Charles Morey 00 (j) .... "' Daytona International Speedway is not a kind '~ track. ~rom its fl~t, winding infield to the <: suspensIOn-bottomIng 31-degree banked trioval t~ms, Dayt0!1a is demanding of both rider and equIpment. When either is less than supe b .th fi' h r . nel er..JnIS . For the AMA Superblke contestants, the challenge is even higher. Unlike the specialized road racers that compete in the Daytona 200, Superbikes were born as something other than all-out two-wheeled Formula One machines. They started as street machines, just like the ones we buy each year at our local Suzuki, Honda and Kawasaki dealers. . The Suzuki Superbike racing effort IS handled by the California _ based Yoshimura Rll!D, headed by Fujio Yoshimura, son of company founder "Pops" Yoshimura. For five consecutive years, Yoshimura Superbikes h~ve won the Daytona event, this year beIng the strongest effort yet with an awesome 1-2 finish at the 19!1l Bell Superbike 100 Season opener. Reigning AMA Superbike Champ Wes Cooley and last year's Daytona winner Graeme Crosby qualified with identical times of 2:07.826, then raced the 100-mile event with Cooley edging Croz by 0.7 seconds at the finish line. Cooley's average speed was 107. 744 mph, compared to Daytona 200 winner Dale Singleton's 108.523 mph winning average. No, the Yoshimura Suzukis are no longer street bikes. They're full-on road racing rockets with a wealth of ingenuity and know-how rolling along on those chubby slicks. Just for fun, we asked Fujio just how much of the stock motor remained. He laughed. "How much is stock?" he repeated, "What's stock is the casesl" The Yoshimura Suzuki! arrive in pieces. First, the stock GSI000 frames are prepared by modifying the rear section, as Fujio put it: "Very controversial, this part." The upper. shock mounts are relocated forward (see photo) by cutting, then rewelding some tubework. Gussets are added along with a new crosstube between the vertical tubes. The steering head and front part of the frame is left stock. A heavily-reinforced box crosssection swingann - one used on Yoshimura's Fonnula One machine last year - is adapted to the frame. Apparently this emphasis on stiffening the rear end is the answer; unlike other Suzuki-based Superbikes, the Yoshimura machines didn't wobble on Daytona's banked tum four. 1!te motor is "95%" built with available parts - crankshaft, pistons, cams, springs and other pieces from the Yoshimura catalog. (The crank is not listed in the catalog, but it is available.) The other five percent is experimental. . S~penslon for th~ Suzuki is "not av~~lable to the public," according to FUJIO, an.d he would not comment on the details of the Kayaba anti-dive forks and rear shocks. They were not ":lass-produced. Each part was VInually hand-built, machined from solid alloy stock. Th~ cor~plete ignition is Kokusan Denki: available from Yoshimura for Suzukls and Kawasakis for ar.ound $600. DY-n,tag three-spoke wheels, the rear one WIth a Suzuki cush-drive kit, are mounted ~ith Goodyear slicks. Brakes are SUZuki RG road racer units in the "standar~" dual. disc on front with a smaller SIngle diSC at the rear wheel confuguration. Pe~ AMA Superbike rules, the fuel tank IS totally stock right down to the locking gas cap. A road racing saddle keeps Copley ?n top of things under hard a~celeratlon. A Nlppondenso oil cooler is utilized to .help keep the over-stressed fourcylinder motor from welding all its par~s t~~ther:. Not presently a~allable, It s anticipated that the unit WIll eventually be marketed as a Yoshimura kit. Mounted ahead of the Wes Cooley autogr~ph model Superbike Bars is a tach WIth a red line painted at 10,500 rpm. According to Fujio, it'll do more and ~till hold together: On the last two laps In the Daytona race, Wes took it up over 12,~00 rpm without hanning the valve tr~In. . Carbu~et.lOn IS handled .by four .31 mm KelhIns, the maxlmum sIze allow~ by AM~.rules and a source of confUSIOn for FUJlo. "Usually you specify t?e size of the carburetor at the ventun; the smallest part of the carburetor has to be 31~. But Honda and Kawasaki 'are USIng the Blue Magnum carburetors... they start off at 34-36mm. Big ca.rburetors..And they put the restnctor plates. In. th~, or sleeves. So, the ventun Size 15, a lot larger on these carburetors. I m sure 99% of the people read the carburetor rule (to be) 31mm. What:s the rule? At the venturi? Or ~ywh~re In the c~buretor 31mm is ~ll n~ht? (~~:4' SImply specifies a maximum sIZe for carbs on fourcylinder motors in Superbike racing as 31mm without being specific where within the carburetor the 31mm is to be measured... Editor.) The Yoshimura Suzukis are allowed to run the small fairings since they are a stock item on the Suzuki GSIOOOS. The standard mold is used, then the headlight hole is filled in. Team Honda's Freddie Spencer won the Talladega Superbike race a week after Cooley topped Daytona. The two are tied in AMA Superbike Series points standings with six events lef~on the calettdar. Can Team Honda catch the Suzuki-supported Yoshimura effort? Or will Wes Cooley successfully defend his title? The year 1981 promises to be the best in Superbike history! 19