Yoshimura history – 12

Yoshimura History #12: The Family’s First Victory in AMA Superbike

1978 GS1000: The World’s Fastest Production Bike

The Yoshimura Suzuki GS750/944 introduced a new era of the superbike with its debut win on September 11 in Rd.6 of the 1977 AMA Superbike Championship at Laguna Seca Raceway. It has finally refuted the 4-cylinder motorcycles’ “powerful but poor handling even on straights” reputation and proved that they could achieve performance as competitive as European twins, such as Ducati, BMW and Moto Guzzi.

Japanese 2-stroke maker Suzuki has boldly staked the future of the company on its first 4-stroke 4-cylinder bikes, and the technological gambit seemed to have paid off as the GS750 was quickly gaining fans on both streets and local tracks across the main market, the United States. However, 750cc 4-cylinder bikes no longer belonged to the top group of the fastest street bikes, as it was then consisted of liter-class bikes.

The leader of the pack was Kawasaki Z1000 (known as the KZ1000 in North America) which was launched in 1976 for model year 1977. Like its predecessor Z1 (903cc with a 66 x 66mm bore x stroke) which it was based on, the Z1000 (1015cc with a 70 x 66mm bore x stroke) became a huge success in the world’s largest North American market.

As in the previous season, Steve McLaughlin once again delivered a debut win for Suzuki. Like the GS750/944, the #83 Yoshimura Suzuki GS1000 was equipped with custom-made KYB front and rear, but now with the 4-into-1 exhaust, the superbike radiates more Yoshimura aura. Also introduced for the 1978 season was the minimum weight limit for each model and the after-race inspection, however, at 425lbs (approx. 192.8kg) with an empty fuel tank, the bike was just 18lbs heavier than the GS1000’s designated minimum weight.

Suzuki’s initial plan for the GS series was to produce the 750 and 550 fours along with the 400 twin, and had no plans at the time to develop sports bikes larger than 1000cc. The company did have an ongoing development project of heavyweight tourer with an air-cooled inline 4-cylinder engine that could be bored out to around 1200cc, but it was expected to have shaft-drive instead of chain-drive giving consideration to durability and maintenance.

Then, in the middle of the project, Suzuki was requested by its U.S. subsidiary to produce a bike that can outperform the Z1000. Etsuo Yokouchi, who was at the time in charge of Suzuki motorcycle development and was also the person who had established a cooperative relationship –––– a partnership –––– between Suzuki and Yoshimura, decided to develop a new 1000cc sports bike instead of a long-distance tourer. The decision was made based on the notion that the new bike could share the basic design and production line with the ¬GS750, and was definitely made with racing victory in mind. If you want to win production races (such as AMA Superbike and endurance racing) you better have a fast sports model!

The bike was designated the GS1000. While the GS750 displaced 748cc from a bore x stroke of 65 x 56.4mm, the GS1000 displaced 987cc with a bore x stroke of 70 x 64.8mm. One of the main design goals was weight reduction of the engine. The kick starter was eliminated during the development. The cam chain idler (gear cushion assembly located between camshaft sprockets) was also eliminated. The crankcase was lightened. Although the elimination of the cam chain idler and the design of the crankshaft (assembled) and clutch unit later became tuning obstacles, the end result was remarkable 232kg of total dry weight (varied according to specification), which was only about 10kg heavier than that of the GS750.

Shohei Kato aboard the #204 Yoshimura Suzuki GS750/944, pushing hard through Daytona infield. Although Shohei was a real gentleman and a very skilled and smooth rider, he was aggressive on the track so much that his riding boots get torn fast (in some cases his toes bled). The red helmet and eyeglasses had been his trademark for years, and the Rising Sun race suit was designed by his wife Yumiko upon entering AMA racing. Seen behind him is the 3rd place finisher John Long’s #36 BMW R90S superbike built by Udo Gietl and Todd Schuster. The two became Yoshimura’s rivals in 1980 when they join American Honda’s superbike team building Freddie Spencer’s CB750F/900F.

The actual development of the GS1000 began in 1977, right after the launch of the GS750. The launch of the GS1000 was scheduled to coincide with the 1978 AMA Superbike Rd.1 at Daytona, which was anticipated to be its racing debut, and needless to say, the tuning and racing of the bike were in the hands of Yoshimura R&D of America (US Yoshimura). A shipment of two GS1000’s –––– camouflaged as modified GS750’s –––– arrived at Yoshimura R&D, just two short months before the debut race. The tuning proceeded in a fast pace.

The AMA Superbike rules changed this year to permit 4-into-1 exhaust, which was a great news to Yoshimura. Original Mikuni carburetors were replaced with 29mm smoothbore Mikuni’s since the use of race carbs (such as Keihin CR’s) was still forbidden, and yet Yoshimura has successfully tuned the bike to produce over 130ps. Fujio was nonetheless concerned about the durability issue, specifically the troublesome clutch and cam chain.

For the 1978 Superbike season-opener at Daytona, Yoshimura R&D prepared three bikes: Yoshimura Suzuki GS1000 to be ridden by Steve McLaughlin who raced the GS750/944 to victory in the 1977 Laguna Seca; Yoshimura Kawasaki Z1 to be ridden by Wes Cooley; and Yoshimura Suzuki GS750/944 to be ridden by Shohei Kato who since 1974 has been running Yoshimura Parts Shop Kato in Atsugi, Japan with his wife, Pop’s second daughter Yumiko. Shohei was also a competitive motorcycle racer who used to race mainly in MCFAJ as his own race team under the name of Yoshimura R&D, but at the time was too busy producing aftermarket parts and running the business as Yoshimura’s Japanese counterpart. Racetracks, for him for a while, has been mostly about product development and coaching young riders, but racing abroad was a years-long dream for both him and his wife. Yumiko had to stay in Japan to take care of their then-2-year-old son Yohei (born November 1975) and their business, so as an expression of her love she bought him a new Kushitani race suit with a Rising Sun on its chest.

The 1978 Yoshimura Kawasaki Z1 was a fruit of family collaboration as it combined Yoshimura engine with Moriwaki frame. The frame, modified by Mamoru Moriwaki himself, did not display any wobbles even on Daytona’s 31-degree banks or backstretch. Cooley took pole position in the season-opener at Daytona with this setup, and then grabbed 2 wins in the same season after changing his bike to GS1000. This combination reappeared later in the 1983 Suzuka 8 Hours.

Mamoru Moriwaki, Pop’s another son-in-law and husband of his first daughter Namiko, also flew over to Daytona after he had perfected the frame modification for the Yoshimura Kawasaki Z1. To eliminate the high-speed wobble which Wes Cooley had for long been suffering, Mamoru increased Z1’s rake (caster angle) to create a greater mechanical trail, and tested the setup himself at Suzuka Circuit to be sure it worked before he sent it to Yoshimura R&D of America.

Friday, March 10, the 1978 AMA Superbike Rd.1 has arrived at Daytona International Speedway. Now with three sons –––– Fujio Yoshimura, Mamoru Moriwaki and Shohei Kato –––– by their sides, Pop and his wife Naoe must have felt so much relieved, especially considering what they had recently gone through. The separation with the Moriwakis. The takeover and reconstruction of their U.S. subsidiary. The fire. And the burn. It was hoped that the family can finally harvest good times.

Finally, after many challenging weeks and months, that priceless smiles have returned to the father and son. From left to right: Fujio, Pop and Naoe. Pop’s sons in law (Mamoru Moriwaki and Shohei Kato) also came over to the States and greatly supported Pop. Note the Yoshimura patch and Moriwaki patch on the chest of Pop’s jacket.

At Daytona, the grid positions were determined by the result of short heat races. The entrants were divided into two groups and each given a heat in the morning, in which Cooley took the pole position and Shohei took the second grid position. Cooley was very happy with the Moriwaki frame, stating “the wobble is gone like magic!” Shohei took full advantage of the nimbleness of the GS750/944 and displayed exceptional riding skills. His talent was real.

The Yoshimura Suzuki GS1000, in contrast, was facing a big trouble and had to retire from the heat. Its crankshaft had broken, much to the team’s concern. Without a pause, Pop, Fujio and Yoshimura mechanics furiously repaired the engine through the noon hour and managed to put the bike on the last row of the grid (34th starting position out of 37 entries) of the main race, just three minutes before it begins.

Shohei, with great clutch control, shot out of the Daytona starting grid, which was located on the wide pit lane. He ripped through the flat infield, tore through the 31-degree banks at the eastern and western ends, and returned to the 18-degree tri-oval in front of the grandstand leading the 1st lap of the race. Cooley was doing great, keeping a strong lead. He checked in 2nd in Lap 1, then switched spots with Shohei on Lap 2.

McLaughlin aboard the powerful and responsive GS1000 charged from the back of the grid to 20th before he entered the main track at turn one, and to 12th before he entered the infield the second time, then to 5th by the end of Lap 2, catching up with the leading group in which Cooley and Shohei were riding. After Shohei’s GS750/944 suddenly grounded to a halt with ignition failure (with a broken CDI base plate) on Lap 3, McLaughlin moved up to 2nd behind Cooley and then dramatically took the top spot by the end of Lap 6.

The two Yoshimura machines were lapping around the 2:15’s –––– roughly 3 seconds faster than the 1977 winner Cook Neilson on Ducati 750SS –––– as they continue to switch spots at the top. At this astonishing speed, which is just about 10 seconds short of the Daytona 200 pole-position lap –––– recorded by Kenny Roberts on 2-stroke 4-cylinder factory machine Yamaha YZR750 (OW31) –––– only a very few production-based bikes at the time could keep up with them.

Cooley and McLaughlin looked set for a 1-2 finish until the second accident happened. No luck at Daytona for Cooley again, a pebble kicked up by the GS1000 had punctured the oil cooler on his Z1 and the race was over for him. McLaughlin, just as he had accomplished with the GS750/944 in the previous season, raced the GS1000 to its debut win. The GS1000, however, came to a halt with a broken clutch during the victory run –––– luckily it didn’t happen a lap before! –––– and had to be pushed to the victory lane. And thus the 13-lap high-speed race around the 3.87-mile course (total of approximately 50 miles) was finished.

“I felt sorry for Shohei,” says Fujio. “Me and Pop were too busy working on the GS1000 and were unable to thoroughly check his machine. He could have won the race. I’m sure that the GS750/944’s overall balance of power and chassis performance was far superior to that of the GS1000 which at that moment was still under development.”

Fujio still regrets it till today. Yoshimura’s 1-2-3 finish in AMA Superbike, and the dream of its first Japanese winner did not come true, but still, they had managed to bring the GS1000 to the Daytona Victory Lane as Suzuki requested.

There was no time to lose because Yoshimura had to prepare for a big race scheduled to take place in Japan that summer, to keep one of the promises that Pop made with Yokouchi two years ago: a victory in a World Championship class race in the 1978 season.

Yoshimura-powered Egli Kawasaki Z2 raced in Japan by Shohei Kato (circa 1976). Yoshimura acquired the Egli frame when the prominent Swiss frame builder asked Yoshimura to barter his frame for Yoshimura Z1 engine. The frame was then fitted with a 69mm-bore 867cc Z2 engine which Fujio built in Japan (before he returned to the States in November 1976 with a new visa) along with a set of race-proven Morris mag wheels which he imported from the States. The bike took pole and 2nd place in a MCFAJ (Motorcycle Club Federation of All Japan) race held at Fuji Speedway with a top speed as fast as the fastest 2-stroke production racers at the time such as Yamaha TZ750, TZ350 and Suzuki RG500.

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Published on August 28, 2020

Stories and photos supplied by Yoshimura Japan / Road Rider Archives / Shigeo Kibiki

Written by Tomoya Ishibashi

Edited by Bike Bros Magazines

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