marine engine digest logo

Yamaha F70 Outboard

Yamaha outboard's four-stroke F70 is so lightweight that legions of them are surely destined to find happy homes rigged on the transoms of aluminum fishing boats, pontoon boats and light fiberglass boats that formerly relied on carbureted two-stoke outboards.

cutaway view of Yamaha F70 outboard

This 70-horsepower outboard motor boasts the best horsepower-to-liter ratio in its class. For comparison sake, it weighs 109 pounds less than Yamaha's four-stoke F75.

Yamah's F70 outboard is founded upon an inline, four-cylinder block. Its four valves per cylinder are actuated by a Single Over Head Camshaft. SOHC versus DOHC translates into less weight and less parasitic losses (friction) from additional valve train component parts. Also, four-valves-per-cylinder, as opposed to just two, frees-up room for bigger intakes valves (a whopping 17-percent) paying big dividends in higher volumetric efficiency. Simply put, the more air that can flow to the combustion chamber, the more horsepower generated. Intake air flows into the F70 via a compact, single-throttle valve and onward to the combustion chamber via with a long-track induction system. Cognoscenti already know the long track boosts low end torque.

The lower unit houses a 2.33-to-one gear set, a stump pulling ratio which boosts low end torque even higher, though theoretically at the expense of mileage and top speed. Not to worry. Tucked into the cylinder block bores are pistons a full 10-percent lighter than previous generation four-stroke outboards. And the significantly lighter reciprocating mass lets the engine rev higher, building more horsepower and a higher top speed. No big surprise, given the state of the art, the Yamaha F70 benefits from an anti-knock sensor that maximizes ignition advance to boost horsepower without endangering piston domes or connecting rods.

Fuel economy is stellar thanks to multi-point fuel injection. There is no carburetor. And again, because Yamaha F70 is a four-stroke outboard motor, there is no need for pre-mix fuel (gas mixed with lubrication oil). Similarly the engine runs quiet and odor free.

artist's rendition of Yamaha F70 outboard motor.

Yamaha's F70 can be fitted with the optional Yamaha Multi-Function tiller handle. Another nice touch, F70 is compatible with Yamaha's Command Link gauges offered in both square and round versions. I like Yamaha's Variable Trolling RPM Control that is usable with either the previously mentioned Yamaha's Multifunction Tiller Handle, or the Command Link tachometer. One must-have option is the Yamaha Customer Outboard Protection. YCOP accesses the Electronic Control Module rendering the outboard motor unable to start without its encrypted electronic key fob. When ordered with the optional YCOP system, Yamaha outboards are delivered with two matched, water resistant key fobs that electronically arm and disarm the system.

You should also know Yamaha F70 outboards spin K-series propellers offered in a broad selection of pitches in order to meet a wide array of applications. Finally, the F70 comes with Yamaha's three-year limited warranty for pleasure use and is three-star certified by the California Air Resources Board (C.A.R.B.) for sale in California.

© Copyright 2011by Tim Banse

Find a local dealership