Cycle News - Archive Issues - 1970's

With stock pipes, the 845cc looks showroom-stock, but screams above 6.000 rpm. It's more pleasant to ride with the Yoshimura exhaust system. Pops lIeft) and Fujio Yoshimura have good reason to smile. Their 845cc GS750 is a winner. heavy-duty valve springs; four Yoshimura /Mikuni 29mm smoothbo re Supercarbs (stock Mikunis are 26mm); cylinder head porting and po lishing and valve lightening; and a Yoshimura four -into-one exhaust system that allows the use of the centerstand. The money buys a motorcycle that is as fast in the quarter· mile as Cook Neilson's AMA Superbike Prod uction 883cc Ducati Desmo was in 1976; a bike that , with the stock pipes. can and has won Open Production at Ontario; a bike that beats all but a few Superbike Production machines in handling. acceleration, and top speed. On the street . we never saw anythi ng that cou ld to uch the ha nd ling/ horsepower combina tion . We tested the Yoshim ura GS750 in two form s. First, wit h the stoc k pipes, and then with the exhaust system . W ith th e stoc k pipes, the bike is the sleeper of the year. T he only suspicious-looking thing is th e set of four velocity stacks protruding from the smooth- bore 29m m Mikuni carbs. As we rode it . the bike looked stock. and. at cruising speeds. sounded almost stock. With no air filters or intake baffling. the machine illustrates just how noisy an intake system can be. At small throttle openings, like when cruising down the freeway at 4.000 rpm and 65 mph . the motorcycle sounds almost as quiet as a stocker. But grab a handful . and a great roar signals the rush of air down the smooth. round carburetor throats. Yoshimura Suzuki 845cc GS750 RPM HP 7,000 65.97 8,000 86.99 9,000 96.98 10,000 99.54 10,500 100.46 11,000 97.81 GS 750 Standard RPM HP 4,000 25.65 5,000 31.91 6,000 37 .80 7,000 52 .20 8,000 58.48 61.1 0 8 ,500 9,000 59 .38 With the stoc k pipes. the bike turned a 12.44 elapsed time quarter mile at 102 mph . Below 6 ,000 rpm , it is impossible to grab a bunc h of throttle without the engine staggering and bogging. Gassing it above 6.000 rpm , or rolling on the gas below 6 ,000 rpm, the motorcycle will surge forward strongly and smoothly. About 7.000 rpm . horsepower explodes the bike forward and rockets the tach needle to the 10.500 rpm .red line as fast as the rider can shift. At the drags . slow starts are made up for by a great rush of high -rpm, higher gear acceleration. With the - hand-bent Yoshimura exhaust system . the bike turned a string of l I -second quarters. ranging from 11.99 to a best of 11.52. ridden by a rider with little drag racing experience. T he exhaust system ma kes a big d ifference on th e stree t, too. At no rmal speeds on the freeway . the ex haust no te is su bdued and non;111111, il'< ' , barely louder tha n wind noise in the test rider's Bell Star helmet. Above 6 ,000 rp m . th e exhaust note is . . . authoritative at best, loud at worst. More important. the engine doesn't stagger when gassed ha rd bel ow 6.000 rpm . After in -town and freeway riding. the spark plugs will foul , and the engine will burble and misfire at lower rpm if the rider grabs a handful of throttle , But if the throttle is rolled on . or if the bike hasn't been just ridden at low rpm . the response is crisp above 3.000 rpm. Below 6.000 rpm . the bike runs like a healthy stocker. Above 6.000. it is a Kg-m 6.75 7.79 7.72 7.13 6.85 6.37 IFt:lb ) (48.82) (56.34 ) (55.84) (51.57) (49.55) (46.07 ) HP 100 90 80 Kg-m 4.59 4.57 4 .51 5.34 5.23 5.15 4.72 IFt·lb) 1 33.20) 1 33.05) 132.62) (38 .62) (37.83) 1 37.25) (34.14) -_J-t 'da nce, Lap tim es im proved as soon as th e rider stopped using the rea r brak e. But thi s is a test of Yoshim ura's engine. not a Suzuki GS750. Apart from the rea r brake. the GS750 enhances the total package. a n exciting. powerful package of horsepower a nd ha ndling , With 100 horsepower. a non offensive (at legal speeds) exhaust note. and the good handling of a GS750. this Yoshimura 845cc motorcycle is a competitive Open class street- based road racer - and a very satisfying street bike. You can get more information from Yoshimura R&D of America. 5517 Cleon Ave .. North H ollywood. CA 91601. (213) 985-2331. • HP 70 C"3;'1!";"* =.-4.:.. ==._/ ' --f--·_·~ w " 29mm Yoshimura/Mikuni smoothbore carbs and velocity stacks roar at large throttle openings. GS 750 Standard Yoshimura Suzuki 845cc GS750 .",-----, " 70 bu llet. Even whe n t he plugs have load ed up after low-rp m riding. the engine will clea r out and ta ke off almost instantly if it is tu rned on over 6.000 rpm . O n the racetrack at O nt a rio Motor Speedway. the bike's horsepower made up for bad starts. blasti ng th rough the pack and into second place (behind another Yoshimura 845cc GS750) before the banking on the first lap. T he hand- bent exhaust pipe, whic h allows use of the centersrand, seriously limited ground clearance on the right side. On the street it was rarely noticeable. but on the track . it soon was ground and smashed into a halfround shape from scraping the asphalt and showering sparks in right handers , Once. when the pipe grounded hard in the fast esses coming off the Ontario banking, the rear wheel broke loose and ' the big Suzuki slid toward the outside of the track. While scary. the slide was controllable a nd the rider did not crash, The hand ling of the big Suzuki m akes a di fference, W hen ru nning on the rac etrack with the ex ha ust baffl e removed. backing off a nd holding a t about ~ th ro ttle would send the engine in to a fit of staggering m isses. The solution was simple - gas it hard or get completely off the gas. In the ory road racers are su pposed to always be either full on the brakes or full on the gas. b ut there are times tha t doesn't quite 'work ou t - like ha lfway around a third-gear sweeper with the exhaust system dragging. May be our test rider needed more courage. The worst part about racing the bike was trying to use the rear brake without locking up the rear wheel . the Suzuki disc is too sensitive. locking up and sending the rear end bouncing and hopping sideways in a frantic ," , .. ~ .. T...- »> 50 Torque Kg-m j~--~-, 50 8 <. ~ ~"" ,,- 40 ..... -.... 7 .. '. 50 ,,' ....."0 Kg-m 6 5 .' 4 30 6 20 6.000 7.000 8.000 9,000 , 10.000 RPM 11.000 4.000 5.000 6.000 7.000 RPM 8.000 9,000 9

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