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The Yamaha Vision (XZ550) was a motorcycle produced in approximately 1982-1983, though a smaller XZ400 model was available in some markets until at least 1987. It offered innovative technology in its motor and bold styling. == XZ550RJ == The XZ550 was the first Yamaha model to feature automotive-style downdraft carburetors with the air cleaner box mounted atop the carburetors, as opposed to most motorcycles' sidedraft carburetors with their side-mounted air cleaners. While downdraft carburetors flow air into the engine more efficiently than sidedraft carburetors, the height of the carburetors and their airbox required Yamaha to design a large tunnel into the bottom of the gas tank. While the tank holds 17 liters(4.5 gallons) of fuel, it looks much larger thanks to the tunnel and suggests that the bike is top-heavy, which it is not. The XZ550 has a water-cooled engine. At the time, some other water-cooled motorcycle engines had fins, intended to suggest the cooling fins on air-cooled engines, cast into their cylinder heads. While fins are absolutely necessary on an air-cooled engine — they increase the surface area of the head, hence improve cooling—they serve no function on a water-cooled engine. By leaving the fins off the XZ550's engine, it simplified the engine's manufacturing process, reduced the amount of metal needed to make the cylinders, and lowered the cost of the engine without affecting its functionality. The Yamaha Vision was originally conceived in the late 1970s when motorcycling was at its peak, and spent three years in development, being overseen by a small group of designers and enthusiasts rather than "committee think". Several high profile external design houses contributed to the design of the XZ550 including GK Design Associates for design, and reputedly Cosworth for the engine and Porsche for the final drive. The initial models were designed to be a performance bike and GK's goal was "to make it into the most advanced super sport bike in terms of both styling and riding performance" To many enthusiasts, the XZ550 succeeded on both fronts, its comfort on long rides and veritable torque-monster engine matched by its distinctive deep V-Twin exhaust beat and endurance race performance. But '82 sales were poor and it was not until the bike was re-invented as a sprot-touring bike in 1983 that sales picked up, although not enough to see the bike surviving. The bike was considered "the closest bike to a B.M.W. ever to come out of Japan" at the time, in reference to its touring credentials and reliability on long-distance runs, generally consiedered "the most European motorcycle from Japan in recent memory." Unfortunately, producing an entirely new product from scratch is never without initial problems, and the Vision suffered from a few. An off-idle carburetion quirk, known as the "Vision stumble", meant the first year machines were prone to initial stuttering on part and full-throttle takeoff. The "Vision stumble" problem, after months of research, was finally solved by racer Marc Salvisberg, who later started Factory Pro Tuning. The problem, it seemed, wasn't a Yamaha development problem at all, but was actually a lean spot, just off idle, caused by what appeared to be residual casting sand that filled the off-idle bleed holes at the throttle butterfly plate in the Weber-style Mikuni carb. That information was immediately relayed to Yamaha U.S., where it was relayed to Japan and verified. The 1983 models carbureted essentially flawlessly. (This claim of a "solution" is disputed by experienced XZ550 forum contributors as a myth - the likelihood that residual casting sand consistently affected the performance of all the 1982 models is highly improbable.〔http://ridersofvision.net/rovforum/index.php?topic=14751.msg135143#msg135143〕 Meanwhile, other riders have successfully overcome the "Vision stumble" in their 1982 models without changing carburettors.〔http://ridersofvision.net/rovforum/index.php?topic=15362.0〕) In the 1982 model, lightning quick steering was considered too extreme for some, though was highly appreciated by sporting riders. The weight distribution was 55/45 and the lightly loaded front end benefited from the installation of a slightly larger than usual front tire. The front suspension was described as too soft, the rear, even with an adjustable shock, difficult to dial in. On the electrical side, the Vision had "a well deserved reputation for eating starters and stators." There is also a problem with the starter clutch. It has a tendency to loose a three bolt fastening in the starter clutch mechanism. The fairing was an option in '82, and that proved to be the bike's downfall, along with being pricier than the other twins of similar size on the market then. But not having the beautiful fairing available at the outset proved the '82 undoing. It was just too unattractive without the fairing. This point came home when all 1000 1983 models sold out immediately...with the non-optional black fairing. The motorcycling public knew a good thing when they saw it..while the marketers did not... The US 1983 model Vision fixed most of the '82's faults, with an improved carburetor eliminating the stumble, air adjustable front forks firming up the ride and improving the roadholding. A non-optional full fairing, with adjustable hot and cold air vents, effectively shielded the rider. With the improved carburetor and minor internal adjustments, the engine's strengths became apparent: it had enormous torque at all revs, and would pull from idle in top gear. Despite the 10,000 R.P.M. redline, the oversquare bore and short stroke kept the piston speed low, with the result that the engine always sounded relaxed, even at peak revs. The exhaust note has been compared to that of a Ferrari Testarossa (which came out several years later.) With its unique "hang support" frame, whereby the engine is suspended beneath the frame for lighter weight, the Vision's performance and roadholding were far ahead of its time. Unfortunately, so too was the cost. The motorcycling boom of the Seventies was already receding before the XZ550 hit the showroom floors, and rival motorcycle companies offered cheaper motorcycles without the quirks. The model was discontinued from sale in the U.S. in 1983, though it maintains cult status online. In current times, the XZ550 has been found to be one of the easiest motorcycles to modify to the owner's personal taste. There are "bobbers", full touring bikes, cafe racers, and general sport bikes in all areas of the world. The online forum for the Vision,www.ridersofvision.net, is a very informative and most complete location for finding repair information, rider help, ride reports and information known to this date. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Yamaha XZ 550」の詳細全文を読む スポンサード リンク
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