Most boats in the U.S. are less than 20 feet long, so while the higher horsepower engines get most of the press, midrange outboards are, arguably, of greater importance to the majority of boaters. The new Yamaha F90B — lighter, smaller and more powerful than its predecessor — is set to make an impact squarely in that midrange space.
Displacement is one of the biggest differences between the F90B and the previous model, the F90A. It has been pumped up to 1832cc, from 1595cc, which allows it to make power more easily and gives it more low-end oomph, for better holeshots and midrange acceleration. Compared to Yamaha’s F70, which has a 1L block, the new 1.8L F90 has nearly twice the displacement, and it matches the displacement of the F115.
Visually, the old and new F90s are noticeably different. The F90A featured a dual overhead cam (DOHC) design; the F90B has a single overhead cam (SOHC) but still features four valves per cylinder. That arrangement gives it a slimmer profi le than the F90A and the F115, which also has a DOHC design. The switch to a SOHC design is largely the reason for the 13-pound reduction in weight, resulting in a total weight of 353 pounds for the 20-inch shaft model. The 25-inch version weighs 362 pounds. The F90B has a slightly higher compression ratio — 10:1 compared to 9.7:1 for the F90A — but it still runs on 87 octane regular fuel. Its 2.15:1 gear ratio puts it in the middle of the pack compared to other outboard manufacturers.
The F90B uses a big-block design and a tuned long-track induction system that leads to a multiport electronic fuel-injection system with four separate injectors to make sure it delivers snappy acceleration. We tested it on Lake Geneva in Wisconsin aboard an Xpress H18B, an 18-foot aluminum center console bay boat that weighs 1,187 pounds dry. Given the H18B’s maximum horsepower rating of 115, a 90 is probably the smallest engine it should use, but it proved to be a good match. One of Yamaha’s best innovations is the Shift Dampener System (SDS), which uses a specially designed rubber hub to smooth the prop into motion without the attendant clunk we’re used to hearing.
With two well-fed Americans on board, the Xpress got on plane in 3.5 seconds, hit 25 mph in 6.4 seconds and reached a top speed of 42 mph at 6000 rpm, and it accomplished its performance relatively quietly. At idle, the only sound I heard was the water from the telltale stream hitting the water. Measuring 57 dBA at idle, and 91 dBA at WOT, it’s really quiet throughout its range of operation.
According to a Yamaha Performance Bulletin on this boat and motor rig, the best fuel economy was at 23.9 mph with the engine running at 3500 rpm. At this speed, the F90 was consuming 3.2 gph, which netted it nearly 7.5 mpg. At 1000 rpm, it was drinking only 0.5 gph, which is good news for trollers, and even at WOT it was burning just 9.6 gph.
The F90B features many of Yamaha’s exclusive features, including Variable Trolling RPM (VTS), which allows drivers to bump their engine speed in 50 rpm increments, from 550 rpm to 1000 rpm, so they can dial in the perfect presentation for lures and live bait when they are trolling. Most F90B outboards will see service with a helm steering system, but buyers can choose a Multi-Function Tiller Handle, which includes a shift lever, power trim and tilt, and control of VTS on the handle.
Buyers can use their original analog gauges for a repower, but the F90 is compatible with Yamaha’s advanced Command Link multifunction speedometer and tachometer gauges, which would allow owners to add the option of another Yamaha-only feature: Y-COP. This is an antitheft device that uses a key fob to disable the operation of an outboard, which is important because Yamaha’s popularity means its engines are the most-stolen brand. If a thief takes it and finds out it won’t start and takes it to a Yamaha dealer to diagnose the problem, that would be a huge mistake, because its technicians are trained to call the police if they are presented a Y-COP-disabled engine.
Even smaller boats these days can be equipped with a wide array of electronics, such as 12-inch fishfinder displays, Power Poles, stereos and livewells, so keeping the batteries charged is a challenge with smaller motors. So Yamaha created a three phase alternator that produces 35 amps of charging power, which is 40 percent more than the F90A. Amazingly, it produces 28 amps at 1000 rpm, so even trolling produces charging.
Yamaha is also making a 75 hp version of this platform, but I’m not sure how it will sell, because of its groundbreaking F70, which weighs 100 pounds less (253 vs. 353). The F70 has less torque, by virtue of its smaller 1L displacement, and its alternator only produces 17 amps at WOT, but it’s difficult to overlook the weight difference, which is a big deal on smaller boats.
The Yamaha F90 is a good choice for boat owners who run in saltwater, thanks to its comprehensive corrosion defense system. It starts with an engine block whose paint job is electro-deposited for superior adhesion. Then, the exterior undergoes a five-part paint process called Phaze Five. Then there’s a redesigned cowling, which offers even greater protection from water intrusion. And maintenance is simple thanks to an easy-access flush-out port that doesn’t require the engine to be running, which the neighbors are going to love.
YAMAHA F90B SPECIFICATIONS
Type Inline four-cylinder SOHC four-stroke
Full-throttle Range 5000-6000 rpm
Weight 353 lbs. (20-in. shaft), 362 lbs. (25-in. shaft)
Gear Ratio 2.15:1
Tested with Xpress H18B
Time to Plane 3.5 sec.
0-25 mph 6.2 sec.
Top Speed 42.0 mph
Decibels @ Idle 57
Cruise 34.4 mph/4500 rpm/84 dBA
Peak 42.0 mph/5600 rpm/91 dBA