Cycle News is a weekly magazine that covers all aspects of motorcycling including Supercross, Motocross and MotoGP as well as new motorcycles
Issue link: https://magazine.cyclenews.com/i/126772
... r------.".-----~~------ --~_:""--------~~----------...,a: ~ ::I: w l%l "" S? a: ~ 11. >l%l (J) o b ::I: 11. Kenny Roberts' OW69 has a 53.5-inch wheelbase and weighs 297 pounds. It's tuned for torque. with four 34mm carburetors and stubby expansion chambers, making 75.9 lb.-ft. of torque and 148 bhp. The frame is squaresection aluminum tubing. with steel stanchion tubes, aluminum fork sliders, and an aluminum swingarm. Wheels are Morris magnesium. tires Dunlop. 1L1m..... DIa"Im_~~' - ----- -------n~.I~Ia"~_ --------- - - - - - - - - - ---------1 --------- ..- - - - - - - ------- --~----. --~-,.,.~- ~ ~-.-.-. ...~ •••: ..,.4:..... -- -- ---nMl~o ----------~------------------ ----- ------- ~~------~~---~ -... ..... ~o~ ~_.- ~ ~ - - - - - -~C ~--~~ v~ ••• ~.. ~. -~---~--~------------ - -~--_....---~ ..o ~ o .--no + S'Eubhp ----- -- By John Ulrich - =~- When Kenny Roberts and Eddie Lawson showed up for the 1983 Daytona 200 with a couple of bright yellow-and-black Yamaha Square Fours, rumors were flying about dis- 22 --~--~ placement of the fast machines. Anybody watching practice I could see that they accelerated harder than anything on the -.--mph track, seemed to spend a lot of time sideways, and had a throatier exhaust note than a typical 500. Roberts won the race, Lawson was second, and afterwards a knot of reporter surrounded the two riders. One asked Roberts, "[s the bike a 680?" (That was one of the numbers flying around the pits). "Yeah, that sounds about right," Roberts said. Ever since, the Yamaha OW69 has been referred to in print , as a 680. Roberts and Lawson, playing along, picked il up and started calling it a 680 whenever they talked to reporters. That "680" is actually 695cc, a 64 x 54mm waler-cooled Square Fourwitb rotary valve induction and powervalve exhausts. And il'S fast. This year Roberts showed up at Daytona and went through a radar trap on the front straight at 178 mph. (Last year thenumberwa 182, but the 1983 version had a narrower powerband. no power-valve exhausts, and more peak power). While the radar said 178 mph, Roberts and Lawson both said their bike gained 1000 rpm after passing the radar trap, before they put on the brakes for the fir t turn. The OW69 redlines alllOOO rpm. It's safe to assume that the bike was al about 10000 rpm in the traps; the 1000 rpm increase is 10%. A correspondin 10% increase in road speed is 17.8 mph. Add that to the 178 mph the radar read, and Roberts was hilling 195.8 mph at Daytona. Roberts is a three-time World Champion; many believe him to be the greatest motor ycle road racer of all lime. But when he first rode [he OW69 during a test session at Laguna Seca last year, he came in shaking his head, telling tire technicians and mechanics at the cene "That thing is fast!" Roberts used the bike to win the 1983 Daytona 200, and was the first man to lap the 3.84-mile course in less than twO minutes. He did it with what Yamaha Racing Manager Ken Clark called "the tractor motor;" a more powerful version of the same engine at in a rate in the pits, just in case. Tractor motor or not, when the race wa over Roberts asked the factory to make the bike easier to ride, trim the horsepower, broaden the powerband. They did it by adding power valves to the exhaust and reducing peak power. So Roberts' OW69 only made 148 bhp when he wheeled it out onto the Daytona course lO pra tice this year. He came back in and had his mechanics back off the ignition timing 2° and make the jetting richer; both reduced power and wheelspin off the corners. Roberts won the race, going the entire 200 miles on a single rear tire. Team Honda's Freddie Spencer and Roberts' Yamaha teammate Eddie Lawson both pilled with tire problems. Besides Roberts, the best-known OW69 pilot is Eddie Lawson, who finished second to Roberts at Daytona last year and fourth this year. "[ don'l even try to explain to people what it's like to ride," Lawson says of the big Yamaha. "Peter Clifford rode a 500 and wrote that compared toa street bike, riding it was likejumping off a moped Onto an RD4oo. And the 680 i a lot faster than a 500. "People always ask me what it's like to ride; bUl what can I tell them? They can't understand. Jt's fast. "At Daytona, Kenny had them back the timing off on it, way off, and made it real lazy off the corners. He wanted to save the tires. He told me about it after the race. But 1 didn't want to do that anyway. I wouldn't have done it. Because knowing how good the tire was last year, [ was going for it. [wanted all the power [ could get. "[ was going by what Dunlop told us la t year after the race, that the tires would have gone another 50 miles. 1 thought 1 could speed it up and make tbe difference. So this year [ gassed it up. Kenny didn't. During the race 1 wondered why he was accelerating