Cycle News - Archive Issues - 1980's

v- l i • cylinder. A Hy· Vo chain on the left side of the crankshaft drives the rear cylinder cam, while identical chain on the right side of the crank drives the forwa rd cylinder's cam. That arrangement allows both cylinder heads (and cylinders) to be identical. simply rotated 180°. which makes for less production and tooling costs. It also puts both intakes in the middle of the V. but staggered. so the CV carbs can be nicely tucked in, the butterfly valve shafts connected and operated by a single cable and throttle stop (or idle stop) screw. Valve adjustment is by screw tappets on the ends of conventional rocker arms. But while actually adjusting the valves should be easy enough, getting to the intake valves looks to be a bitch. They're in the middle of the V, remember, and fitting in those carburetors so neatly didn't leave much room for fingers and feeler gauges. The cam chains have automatic tensioners and the ignition is electronic. The whole engine is only 15 inches wide, narrower than the ultra· narrow Seca 550 engine. which is 16 inches wide. The wet·sump engine is a stressed member of the frame, the head bolts on the forward cyl;nder extending upward to attach to a hanger plate underneath the steering head. Since the engine is stressed, solid metal head gaskets are used, so to avoid oil leaks the valve train is fed by external metal oil lines. The frame itself is a giant, stamped· steel arrangement forming a huge, sealed, hollow backbone which serves as an airbox. The carburetors are fed from rubber tubes leading into the backbone, and back behind the engine a foam air cleaner bolts over a cutaway in the backbone. near where the frame meets the swing. arm pivot. The swingarm is a triangulated piece that attaches to the Yamaha monoshock hidden up under the seat and gas tank. The left side of the swingarm carries the drive shaft, and the swingarm pivots on tapered roller bearings. Monoshock damping is adjustable by turning a knob located underneath the right side of the seat. The front forks can be adjusted with air pressure, and carry a single msc brake. The rear brake is an internal expanding drum. The exhaust system uses two mufflers with a large expansion box between them. The forward cylinder feeds exhaust gas through a shiny chrome head pipe into the right muffler and expansion box, while the rear cylinder dumps exhaust directly into the middle of the expansion box through a nat· black pipe, hidden by the side panels. Alright, by now everybody is wonder· ing when we get to the good part, whkh is how she goes, as it were. Well, to start with, we've gatta talk about V·twin pow' er, since that's what this beauty is, a V· twin. It sounds like any other V, whkh is puzzling. To hear the Yamaha peo. pie tell it, this one has an unusual firing order. They say that one cylinder fires on each (360°) crankshaft rotation. Har· leys fire on a staggered pattern (315°, 405°, 315°, etc.) resulting in that lumpi· ty·lump sound. But the Yamaha still sounds staggered in firing order (proba· bly 285°, 435°, 285°, etc., since it's a 75° V) and acts like it, too. It certainly isn't firing like a 180" vertical twin, that's for ~ ~-----:l~-----o_----=----------a...E An in-line four cylinder engine coupled with cafe styling makes the Seca appeal to the go·fast crowd. (Left) Twin discs with a special cut up front make stopping easy. (Right) Clean styling with competitive power. sure. The redline on the engine is 7000 rpm. which might lead one to believe that this engine is a real torquey mother. Just like a Harley. It isn't so. Yamaha remember, is the company that built all those fast two strokes and the peaky Secas and before that the TX500, and they believe in rpm as a means to power. Which means that even this, their great effort in producing low·end torque, is a lot like their previous great low·end· torque effort, the TT500. The engine likes rpm. It·s possible to lug the thing around at, say. 2000 or 2500 rpm. but only a fool who misses the point and has weird dreams about the Harley he didn't buy would admit such a thing. Anybody with empathy for machinery will quickly catch on that this engine likes to turn above 3000, is happier around 4000 and accelerates its best above 5000 or 5500. It accelerates, too, about as hard as the Seca 550 (low 13'second or high 12·second quarter miles) with 75% of the revs, and, to a twin·cylinder man, a much better sound and feel. It cruises at 60 mph with a little more than 4000 rpm, and is dead smooth at that speed, the mirrors perched on the rubber· mounted bars crystal clear and the rubber· mounted foot pegs transmitting no vibration. Run it faster and it starts to shake a little, nothing like a Harley, but more than a Ducati, and more than a four· cylinder , but not really bad at all, not even up near redline, which it pulls in fifth gear easily. All the while the shaft drive is unobtrusive and non·objectionable, maybe being the best Yamaha has ever done in dealing with the problem of avoimng drive· line snatch and shaft· torque· up in a motorcycle. The engine crankshaft rotates clockwise across the frame, like the XSII has eight times the snatch and three times the torque re\lction, so how can you figure' it? Anyway. In the face of low·12. second 750cc four·cylinders, the Virago is not fast. But it is plenty fast enough for actually riding down the 15

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