Photos by Terry South.

Two things a motorcycle manufacturer has to look out for when introducing a new model: the competition and the economy. Yamaha got the competition right when it introduced the XJ550 Seca in 1981, as mid-size bikes had not been very popular during the horsepower wars of the late 1970s. Honda had recently upsized its rather boring CB550 to the CB650, while Suzuki?s GS550E had been around for quite a while. Newish but not dazzling was Kawasaki?s KZ550, which was soon slightly hotted up, with problems, for the GPZ550 version.

While this new Yamaha was the cat?s pajamas…to use a 100-year-old phrase that means it is doing what it is supposed to do extremely well. The engine had been around a while, with all problems sorted out, an in-line four with two shim-adjusted valves per cylinder and two chain-driven overhead camshafts. One tricky bit was this new YCIS ? or Yamaha Induction Control System ? a rather complicated addition to the cylinder heads that was intended to improve combustion and also mileage. The main fuel intake would move along calmly and rapidly between carburetor and combustion chamber, until it met the YICS just above the valve. These sub-intake ports were all connected and would send fuel remaining in the other intakes into the carb?s cloud of fuel at a very fast rate, improving the firing chamber swirl. The better-burning also meant better mileage, and Yamaha was getting more than 50 mpg with the 550.
But we?re ahead of...