Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
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--------------,----------,z o II) ,~ ~ 9 o z < a: < J: w III '" u iE £ , Wes Cooley on the Yoshimura Suzuki at Riverside, 1984; using hard riding to braak up the ranks Of Hondas. Inside Wes Cooley's Yoshimura Suzuki By John Ulrich Privateer, or factory? The image. associated with a racing privateer is a rider working on, his own bike in the back of his .van, paying his own bills, living from race to race. And the image most have of a factory team is an IS-wneel race transporter full of exotic bikes built of unavailable parts and a squad of salaried mechanics attending to every whim of highly-paid riders. In truth there are dozens of variations between those two strong images; privateers with paid mechanics and nice transporters and significant sponsorship help; privateers with a friend working as mechanics for no money or a cut of the purse; privateers getting back-door help and maybe some money from one factory or the other. But what is Yoshimura R&D of America? A factory team? They've been associated with Suzuki for so long that at times they appear to be, a t the race track an yway, part of the company. But in 1984 Yoshimura did not receive direct financial support from Suzuki; instead, the company gave them parts for use in their racing effort; the technology used to build their GS750 was developed by Yoshimura in japan and in Chino, California. Consider the machine, a GS750 Suzuki ridden with distinction by Wes Cooley at Riverside (he finished second behind Team Honda's Fred Merkel); at Laguna Seca (he took the lead as the race was red-flagged; scoring was backed up one lap and hewas credited with second behind Merkel; then his bike weighed-in too light and he was disqualified); .at Sears Point (he won after Merkel crashed) and at Willow Springs (he finished a close second to Merkel). It doesn't take long to find trick parts'on and in this motorcycle. :The rods are forged titanium, made in japan to Yoshimura specs. The pistons are also japanese forgings Yoshim.ura bought Mahle forgings from Germany until they found a suitable supplier in japan. But while exotic and expensive, those parts and other trick components on the motorcycle - are not unobtainable. Yoshimura R&D of America will sell the same parts to anybody with the money to pay for them. The same goes for the KYB racing forks, developed without anti-dive, with 40mm stanchion tubes. They're air-assisted and spring preload is adju.stable within a 25mm range. The aluminum triple clamps are milled out of aluminum, by Yoshimura of japan, a racing parts Iabrication and manufacturing facility run by Pops Yoshimura and bis son, Fujio on the outskirts of Tokyo. The fork brace is also made and sold by Yoshimura. The stainless steel discs - drilled up front, drilled and laterally ventilated in'the rear - are works Suzuki parts, as are the magnesium calipers. But those pans are sold through Yoshimura. . Other pans are less exotic - 33mm Mikuni smoothbore carbs, the front side of the slides notched for beuer low-end response and less vacuumcaused slide stiction; two oil coolers. one from Earl's Supply mounted behind the ventilated number plate, one from Nippondenso mounted on the frame downtubes. And instead of developing and using an expensive dry clutch, Yoshimura mechanics installed a clutch from a 1978-79 two-valve GS750, which has six springs and 13 plates compared to the four-valve GS750s four springs and 12 plates. The other trick stuff? All available from. Yoshimura. Like a new rear shock linkage for a smoother progression curve and a less-harsh transition between damping rates. And external braided steel oil lines feeding the rocker arm shafts, needed beca use the usual Yoshimura trick of mounting Kawasaki KZ900cam chain roller sprockets in the cylinder head makes it impossible to u'se the standard cross-over steel oil feed tubes positioned under the cam cover on a stock engine. The cam chain? A heavy-duty Yoshimura part. The CDI? Made by Kokusan Denki for Yoshimura, complete with a cast magnesium mag cover emblazoned with the Yoshimura logo. Wes Cooley won't be riding this motorcycle in 1985, one he made famous by his hard riding - he and Yoshimura have gone their separate ways. But the machine will'see use in 1985 anyway, ridden by new young find Kevin Schwantz; meanwhile, Pops and Fujio are hard at work on a GSXR750-based Superbike, and racing engines have already been developed and well-tested in a cooperative program involving Yoshimura and the Suzuki factory. • Yoshimura Suzuki Engine type •.. . . . . .• Air-cooled Calculated speed in gears at redline (geared for Willow Springs) DOHC. inl.ine-four . Bore x stroke. . . . . . .. 67x53mm 5th :.149mph Displecement .' 748cc 4th 125 mph Compression retio 12.3:1 3rd 106 mph Carburetion (4) 33 Mikuni . 2nd' 90mph HorMpOwer .. .. .. .. ... 118 bhp 1st 72 mph @11500rpm Rake 27O Torque 57.8 lb.-ft. Trail 4.5 in. @9OOOrpm Front suspension type , KYB Valves per cylinder 4 racing forks Intake valve size 26mm Fork tube dillmater 40mm Exhaust valve size 23mm Front wheel travel 5.1 in. R. .r suspensions type Intake lift 9.0mm Fox Exhaust 11ft 8.8mm twin-clicker shock Included valve angle 200 RNr wheel travel 5.5 in. Intake valve timing 280-48° Front brakN (2) 13 in. di_ Exhaust valve timing 600-18° Reer brake" 9 in. disc (measuring pt.) 1mm Frontwhe" 4.00x18 Ingnition KokuAn Denki COl Campagnolo magnesium Rear wheel. Lubrication Wet sump 3.50x18 Redline 12000 rpm Campagnolo magnesium .rpm. @ 60 mph •...... 4832 rpm Fronttira 3.25/4.25-18 Gear ratios Dunlop KR 133 Primary 1.90:1 (91/48) Rurtire 3.75/6.50-18 Final 3.14:1 (44/14) Dunlop KR133 5th 1.04:1 (25/24) Dry weight 397 lbe. 4th 1.23:1 (27/22) Wh. .lbeM 58.3 in. 3rd 1.45:1 (29/20) 5.5 gal Fuel capacity 2nd 1.72:1 (31/18) Ground clearance 4.7 in. 1st 2.13:1 (34/16) Seat height 32.3 in. (Below. left) Forged titanium rod on the left is 117 grams (4 oz.) lightar than the stock steel rod and cap bolts (not shown) screw upwards into rod body without using nuts. (Below, right) Forged·Yoshimura piston has one compression ring, one oil ring and is domad; standard piston on right of photo is flat-topped.