Yamaha?s latest addition to its four-stroke stable, the F115, fulfills a promise to continue expanding its impressive four stroke line into the new Millenium.

Topping last year?s F100 outboard, the new 115-horsepower for 2000 uses an in-line, four-cylinder block that displaces 1,741 cc. It produces its maximum rated power at 5,500 rpm and has a full-throttle rpm band of 5,000 to 6,000 rpm.

The same double-overhead camshaft, 1,596cc block used for the F115 also powers Yamaha?s F100 and F80, as well as the new Mercury/Mariner F90 and F75. The increased displacement comes from a bore and stroke of 3.110" x 3.495". That means the F115 has the same bore as the other engines, but a longer stroke.

The double overhead camshaft (DOHC) operates 16 valves, two inlet valves and two exhaust valves per cylinder, and should ensure optimum cylinder breathing. Feeding the system are individual air induction pipes plus four separate throttles and injectors, which offer precise adjustment of fuel/air mixtures entering the combustion chamber. Unlike the rest of the Yamaha four-stroke models, this flagship engine features an electronic multi-port fuel-injection system in place of carburettors. The system is monitored and controlled by an onboard micro-computer.

The F115 has power trim standard, and is offered in 20" and 25" transom heights. The lightest of the two models weighs just 398 pounds. The F115 breaks new ground in four- stroke outboards: It is the first to be offered as a counter-rotating model using a left-hand pitched propeller for twin installations. (This model is only available only with a 25"-long shaft.)