Cycle News - Archive Issues - 1980's

1""""4 c<") l-< Q.) ,.0 o .... u (Above) the XJ700 Maxim econo-cruiser; (below) the remote adjustment system for the FZ750 sportbike'ssingle-shock rear suspension. The XJ700X Maxim is a hi-tech cruiser, including five valves per cylinder and water cooling. It's a tariff-buster. V-Max instruments include speedometer on bars, tach and temperature gauge on psuedo-tank. New barning in the FIIIOO's level sensor prevents the low-oil-level warning light from coming on during hard acceleration, and a new notch in the carburetor slides improves lowrpm response. The anti-dive system built into the FIII00's front forks has been revised so the compression damping rate increases more, sooner. The only 750 in Yamaha's 1985 stable is the water-cooled FZ750, detailed in Cycle News, October 3. Since the sport bike's introduction at the Cologne, West Germany show, Yamaha has released more-complete specifications. The FZ750, which Yamaha press materials tout as being as close to race-ready as any street machine sold, has a 58.5-inch wheelbase, 260 rake and 3.82 inches trail. Seat height is 30.7 inches. The front tire is a 120/8016, the rear tire a 130/80-18. Front wheel travel is 5.5 inches; rear wheel travel 4. 7 inches. Fork stanchion tubes are 39mm in diameter; the tubes have thinner walls above the lower triple clamp, to reduce weight. The front section of the gas tank is hollow to accommodate the airbox and air cleaner, and the rear section of the tank extends down almost to the top of the crankcases. Fuel capacity is 5.3 gallons; because the gas level is lower than the carb float bowls, an electric fuel pump is used. The combination of the FZ750's five-valve hemispherical combustion chamber and concave piston produces a spherical shape which Yamaha engineers say allows more compression without detonation. Compression ratio is 11.2: I in the 75Occ, 68 x 51.6mm engine. _ The_~ tt~~ ~ pJain-~,!rjng_q~fJk- shaft with gear primary drive - the gear machined into cylinder number three's outboard flywheel. Nothing is mounted on the end of the crank the FI IIOO-style plug-in alternator is behind the crankshaft.. The clutch is hydraulically-activated but uses six coil springs instead of a diaphragm-type spring used in many machines with hydraulic clutches. Coil springs don't have a diaphragm-spring "over-center" effect and thus are more predictable and less grabby at the friction point; coil springs are better for racing applications. The six-speed close-ratio transmission can be removed without taking the engine out of the frame or splitting the crankcases. Instead of a conventional crankshaft-mounted ignition, the FZ uses two small sensors built intothe crankcases - one on each side - trigger.ed by a notch in each outboard crankshaft flywheel. The sensors are small enough so they add no width to the engine; advance is electronically controlled. The dual camshafts are driven off the center of the crank by a roller chain; the intake cam has 12 lobes and nine bearing towers; the exhaust cam has eight lobes and five bearing towers. The cylinder head is built-up in three pieces, the cams and shimunderneath bucket-style tappets riding in the middle section, which fits between the main cylinder head assembly and the valve cover. Thatconstruction allows the cylinder head to be removed with the engine still mounted in the frame. The valve cover is magnesium, uses a rubber gasket and is secured by eight bolts. _ Xaf!l~tta ~f}gin_e~rs_say !~at_t~e cC?r.n- V-Max fuel tank is underneath the seat; hinged seat back allows access to locking cap. pany will guarantee a long service interval on valve lash adjustment. The FZ's four downdraft Mikuni CV carbs are nominally 34mm; but the carb bores are actually figureC8 compound ovals. The exhaust headpipes are single-wall stainless steel to reduce weight compared to conventional dual-wall steel head pipes. Head pipes for cylinders one and four feed into the right-hand collector; cylinders two and three feed into the left-hand collector. To reduce frictional losses the FZ has less piston ring spring pressure than usual; to cut power losses to crankcase press ure there are large breathing holes cut into crankshaft support webs. The FZ's full gallon of oil is also carried lower in the crankcases relative to the crankshaft position, to reduce drag caused by the crank plowing through standing oil. The engine is solidly mounted in the rectangular-cross-section steel frame, and the down tubes unbolt to simplify se.rvice. Needle roller bearings are used in all pivot points for the single-rear-shock linkage system. The rectangular, aluminum-alloy swingarm is wide to accommodate racing slicks; the 530 O-ring drive chain's sprockets are similarly offset to allow tire clearance. The one-piece, frame-mounted fairing is made of plastic with a polycarbonate windshield. Side vents in the fairing are designed to pull hot air out and around the rider to avoid the baked leg syndrome. For riders who want to race the FZ750 in a larger displacement class, Yamaha engineers say the engine can be bored to 9OOcc. Weight figures aren't available, but the feel a rider gets from si lling on the FZ750 is that of a 600 - this is a small, light motorcycle. Next in line in terms of displacement is the 697cc, water-cooled XJ700X Maxim, a stylish cruiser that shares the FZ750's five-valve -percylinder bllt has conventionallymounted, behind-the-cylinder-head 33mm Mikuni CV carburetors. Bore and stroke are 68 x 48mm, compression ratio 11.2: I. The Maxim X engine is rubber mounted and uses a lower end based on the XJ900; like the X1900, the Maxim X has shaft final drive. Wheelbase is 59.8 inches, rake and trail 31.5 0 and 4.72 inches. The front tire isa 100/90-19, the rear a 130/90-16, mounted on cast aluminum alloy wheels; the rear wheel i~ similar to that found on the V-Max. Fuel capacity is 3.4 gallons. The X]7OO Maxim, on the other hand, is an air-cooJed, 696cc, 65 x 52.4mm economy cruiser, a continuation of the pre-1985 Yamaha cruiser line. Yamaha's two Virago V-twins have more Harley-like styling this year, with added chrome. The XV700 Virago is a 699cc tariff-buster; the 981cc VlOOO is a heads-up cruiser styled to compete with Harley-Davidson's 1340cc line. Both Viragos have staggered duel exhaust pipes and enough chrome to blind a casual spectator. The sporty FJ6oo, which, contrary to whata monthly magazine recently printed in naming the 10 best bikes of 1984, completely dominates its road racing classes nationwide, has a larger reartire (120/90-18 from 110/90-18) and suspension and chain guard clearance to match. The RZ350 is California legal for 1985 thanks to the addition of catalytic converter mesh in the headpipes, where it gets hot 'enough at lowenough rpm to make the RZ350 pass the city-driving emissions standards for that state. With the addition of catalytic materiaJ to the head pipe, one bunch of mesh has been removed from the mu[flers. • o 19

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