Yamaha FX140 PWC: Strokes of Genius

Yamaha's FX140 four-stroke personal watercraft is a major achievement.

17th November 2001.
By Matt Trulio

img6288Mark Speaks, president of the Yamaha Watercraft Group in Newnan, Ga., doesn’t waste words. Nor does he exaggerate, at least in front of the marine writers he faces each summer at Yamaha Watercraft’s annual media introduction.

So when Speaks described the four-stroke FX140 personal watercraft as Yamaha’s “most important new model since the original WaveRunner in 1986″ to members of the marine press August 20 in Savannah, Ga., he got everyone’s attention. For Speaks, that was a bold statement, bordering on audacious.

It also happened to be true.

Let the faithful at Yamaha and Sea-Doo argue over who introduced the “first” four-stroke watercraft (a Sea-Doo four-stroke also was unveiled to members of the marine press August 20, leaving everyone wondering how to be in two places at once). The fact is that, come 2002, two four-stroke models will be available to consumers. (Make that three — Honda will introduce a four-stroke watercraft this fall.) And that’s very good news to everyone, because it’s likely the final stage in the evolution of clean and quiet personal watercraft.

The Yamaha FX140 reportedly cuts emissions by 75 percent over carbureted two-stroke models of similar horsepower. According to the people at Yamaha, the four-stroke model more-than-meets Environmental Protection Agency emissions standards for 2006 and California Air Resources Board emissions standards for 2007.

Power Moves

The four-stroke MR-1 motor in the FX140 is based off Yamaha's R-1 motorcycle engine.

The four-stroke MR-1 motor in the FX140 is based off Yamaha’s R-1 motorcycle engine.

Carbureted two-stroke engines initially were chosen in the middle to late 1980s for personal watercraft for the same reasons they were chosen for motorcycles, snowmobiles, outboard powerheads, lawnmowers and leaf blowers and more. Two-stroke motors are compact and lightweight, and have a superb power-to-weight ratio. Plus, they make power quickly, which translates to the kind of instant throttle response preferred in the aforementioned products.

Four-stroke engines, on the other hand, tended to be significantly larger and heavier than their two-stroke cousins. And while known for delivering steady power throughout their operating ranges, they didn’t deliver the same instant “power blast” as two-strokes.

Carbureted two-stroke motors made sense in watercraft for another reason: their lubrication systems. In carbureted two-stroke motors, oil is mixed directly with the fuel. That means that even if turned upside down — not an uncommon occurrence in watercraft riding — the engine would receive proper lubrication.

That lubrication system also happened to be the most serious downfall of all carbureted two-stroke motors. Burning oil in fuel produces higher-than-acceptable (at least in the eyes of those at the EPA and CARB) emissions in the air, as well as discharging a substantial amount of unburned fuel and oil into the water.

Four-stroke motors, at least those available at the time, held oil in a reservoir at the bottom of the motor where it was most needed. (The oil was not mixed directly with the fuel.) That works well when the motor is right side up. But turn a conventional four-stroke motor upside down and the oil runs to the top of the motor, leaving critical bottom-end engine components unlubricated.

Direct fuel-injection systems for two-stroke engines were the intermediate (or permanent, in the view of some DI proponents) solution for personal watercraft manufacturers. Direct-injection two-strokes reportedly reduce emissions by 60 percent over their carbureted two-stroke counterparts, and according to watercraft manufacturers some direct-injection models meet EPA 2006 and CARB 2007 emissions standards. Still, four-stroke-engine-powered watercraft remained a major goal.

Inside the MR-1

The toughest trick for the engineers at Yamaha was developing a four-stroke fuel-injected motor that delivered all the power, weight, size and lubrication benefits of a two-stroke motor. Based off Yamaha’s successful four-stroke R-1 motorcycle engine, the first generation of the MR-1 was installed in test watercraft in 1998. A number of versions, not all successful, followed.

“We tested a lot of ‘bad,’” said Scott Watkins, product manager for Yamaha Watercraft. “We went through something like 15 to 20 generations of this vehicle to get where we are today. We spent something like $10 million on development.”

The final version of the MR-1, at least for 2002, is a fuel-injected, water-cooled four-cylinder motor with double overhead cams, 20 valves (five per cylinder) and independent water-jacketed exhaust manifolds. The compact liquid-cooled engine develops 140 horsepower. For lubrication, the engine employs a dry-sump system with two oil pumps and, perhaps most crucial, a backflow protection system. The system incorporates an electronic slant protection switch that stops the engine and oil pumps if the watercraft is overturned. To reduce weight, the MR-1 was designed with a one-piece cylinder and crankcase assembly.

To get the horsepower they wanted, Yamaha’s engineers knew they’d have to make the engine run at relatively high (7,500 to 8,000) rpm. For the engine itself, that posed no major problems; however, a pump spinning at the speed would be inefficient. To reduce the speed of the FX140′s 155mm Hyper-Flow pump, Yamaha installed a driveline reduction gear box with a 1.47:1 ratio.

Additional highlights of the MR-1 motor include a high-volume intake box with a water-repellant air filter and flame arrestors, a computerized engine management system, a thermostatic and pressure-controlled cooling system, a corrosion protection system with zinc anodes and electronic variable ignition timing.

The hull and deck of the FX 140 are made of sheet molded compound and were, according to Watkins, designed especially for the four-stroke motor’s performance traits and balance characteristics. The hull has a “stepper draft V-hull” and “performance sponson design.” At least in Yamaha’s theory, those design characteristics would provide exceptional maneuverability and a dry and comfortable ride.

Proof in the Ride

All of this information, though explained in greater detail by the Yamaha folks, was in the press kit handed out at the evening presentation August 20. The proof would come in the following day’s ride.

Jeff Hain, senior editor of Personal Watercraft Illustrated (the most technically thorough consumer publication in its market) and I started testing early the next morning on the Savannah River. Hain hopped on the FX140 and I, for purposes of comparison, rode a 155-hp Yamaha XLT1200.

The first thing we noticed about the FX140? The near absence of engine noise. At idle, the MR-1 motor operates so quietly you can easily forget it’s running. At low, middle and full speeds, you can hear the engine running, but the dominant sound is the boat’s hull moving through the water. Pull the seat off the FX140 and goose the throttle and it sounds like an R-1-equipped Yamaha motorcycle. And that’s a lovely sound.

Demonstrating impressive throttle response, the FX140, accelerated powerfully out of the hole and all the way through the mid-range. In fact, it may well be the smoothest accelerator in the Yamaha stable. Matched against the more powerful XLT1200 in an informal standing-start acceleration test, the FX140 stayed even until it reached the last 10 to 15 percent of its operating range, when the XLT1200 began to pull away. But not by much.

Running with the current of the Savannah River, the FX140 reached 56 mph. Against the current, the watercraft hit 54 mph. That’s certainly within acceptable standards for today’s three-rider watercraft.

When it came to handling, however, the FX140 was beyond acceptable. The new hull, as advertised, carved smoothly and knifed through chop. Throughout the engine’s operating range, the power output was smooth and consistent, and that made it easy to maintain consistent speeds through corners. On exit with the throttle wide open, the watercraft accelerated quickly and — here’s that word again — smoothly to top speed.

With Hain driving and a Yamaha staffer observing, I took several wakeboard runs behind the FX140. Given the consistent nature of four-stroke power, I expected the FX140 to be an exceptional watersports towing machine. (The common complaint about two-stroke watercraft, where power can be “peaky,” as towing machines is the difficulty of speed control.) It was — and wasn’t.

First, the good news. The watercraft had no problem popping me, a 180-pound rider, out of the hole. The first start actually slammed me so hard that before the second start I asked Hain to go easy on the throttle — not a frequent request from wakeboarders behind watercraft. Once I reached the speed I wanted, Hain had no trouble holding it. Speed control was tournament tow-boat perfect, the best of any watercraft I’ve ridden behind.

The not-so-good news? I had no trouble pulling the FX140 off line.
The driver and observer complained about the lateral roll I created in medium-hard turns, and in my hardest cuts I could force the FX140 to bow steer. To be fair, lighter and less aggressive wakeboarders likely would affect the watercraft less dramatically.

With the exception of the well-intentioned though awkward placement of the in-dash reverse handle and downward sloped platform, which looked great but made putting on a wakeboard an act of contortion, the FX140′s ergonomics were flawless. Saddle padding and shape, at least to my tastes, were plush and perfect. And the five-position adjustable handlebars made it easy for drivers of all shapes and sizes to find a comfortable riding position for extended touring. Plus, the FX140 is a true three-seater, meaning it can handle three riders without making them feel a little too cozy, and without tipping excessively at low speeds.

The people at Yamaha deserve applause for the four-stroke FX140. It’s not a perfect model, but its strengths far outweigh its weaknesses. With all apologies to Sting, it’s a brand new day for personal watercraft, one in which FX140 shines brilliantly.

Yamaha FX140 Specifications

Overall length 131.5″
Width 48.4″
Seat length 66″/56″
Dry weight 798 pounds
Rider capacity 1-3/ 529 pounds
Hull material Sheet Molded Compound
Engine type Four-cylinder four-stroke
Displacement 998cc
Horsepower 140
Compression ratio 1.4:1
Lubrication system dry sump
Cooling water
Ignition TCI
Transmission Direct drive from engine
Pump Axial flow single stage
Impeller Three-blade stainless-steel
Fuel capacity 18.5 gallons
Oil capacity 1.32 gallons
Storage capacity 26.42 gallons

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About the author:

Matt Trulio

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Matt Trulio is the co-publisher and editor in chief of speedonthewater.com, a daily news site with a weekly newsletter and a new bi-monthly digital magazine that covers the high-performance powerboating world. The former editor-in-chief of Sportboat magazine and editor at large of Powerboat magazine, Trulio has covered the go-fast powerboat world since 1995. Since joining boats.com in 2000, he has written more than 200 features and blogs.
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