Review: Yamaha F6CMHS outboard motor

By: Andrew Norton

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The Yamaha F6C is now the most powerful single-cylinder four-stroke portable outboard available, reports Andrew Norton.

Review: Yamaha F6CMHS outboard motor
At wide open throttle, vibrations on the Yamaha F6C outboard motor were only slightly higher than on the twin cylinder F9.9F engine – a remarkable comparison.

Originally published in TrailerBoat #258, June / July 2010

The portable F6C is Yamaha’s first single-cylinder four-stroke six and is the most powerful of a trio of four-stroke outboard motors from 4-6 horsepower. They are all made in France, a logical step since Europe is the biggest market for them.

Using components from the long-running two-stroke Yamaha 5C, such as the lower unit and transom brackets with five trim and three shallow water drive-positions, the Yamaha F6C also has the same long steering tube as the four-stroke Yamaha F4A that was released on the Aussie market a decade ago.

But unlike the portable Yamaha F4A, the Yamaha F6C outboard has pressure lubrication, decompression starting where the exhaust valve is opened slightly on initial starting, and the availability of a 12V charging circuit. Other features include an auxiliary prime pump to supply the carbie from the integral fuel tank after extended periods of disuse; a fuel filter in the neck of the integral tank; and a three-way valve for either closing the fuel-cock or allowing fuel to flow from the integral tank or optional plastic remote tank.

 

YAMAHA F6

The unit’s tiller-arm folds back alongside the upper cowl and a dual push-pull throttle-cable is used for reliability. Unlike the direct competition, the Yamaha F6C portable outboard motor can be stowed on either side, a useful quality if it is transported in a small car boot. Large handles fore and aft also make carrying the F6C easy, another useful addition since it’s the heaviest of the four-stroke sixes.

Yamaha has obviously used the Suzuki DF6 outboard as a reference point and improved on the idea. At 139cc the piston displacement is only 1cc greater with the same bore and stroke measurements. However, the Yamaha F6C develops a full 6.0hp at only 5000rpm compared to 5.9hp at 5250rpm for the Suzy. The Tohatsu 123cc four-stroke MFS 6B and Mariner/Mercury F6 engines also develop 5.9hp at 5500rpm.

Like Yamaha’s brilliant four-stroke F9.9F, the Yamaha F6C has extremely long service intervals, with servicing required every 100 hours or annually after the first service at 20 hours or three months. Valve clearance adjustment isn’t needed for the first 500 hours, whereas with the DF6 it’s every 200 hours, and 100 hours for the MFS 6B/F6 engines.

 

PERFORMANCE ON THE WATER

Grant Binskin from Yamaha Motor Australia had supplied me with a pre-production Yamaha F6C for extended evaluation. The engine was mounted on my flat-bottomed Sea Jay 3.4 Punt to compare directly with a DF6 I’ve been evaluating for seven years and carefully run-in according to Yamaha’s recommendations. By the end of the first week a total of seven hours had been clocked up, with another three to go before the engine could be subjected to extended trolling trials.

Due to the choke not being crosslinked with the throttle, unlike the DF6, cold starting was a bit "hit or miss". However, once fired up, the thermostatically-controlled F6C warmed quickly and settled down to a surprisingly smooth 1500rpm idle. No oil smoke appeared at any time using standard 91 RON unleaded petrol and Yamalube 4 oil.

Pushing a total of 290kg including two adults and fishing tackle, and spinning the standard 8.25in pitch semi-weedless alloy prop, the Yamaha F6C planed us at 21.4kmh (11.5kts) at 4700rpm and three-quarters throttle opening. The WOT averages were 29.7kmh (16.0kts) and 2.3lt/h at 5570rpm. The DF6, pushing the same load and spinning a seven inch alloy prop (the gear ratio is 1.92:1), planed us at 22.4kmh (12.1kts) and 5000rpm, and averaged 28.0kmh (15.1kts) and 2.6lt/h at 5690rpm.

But the biggest difference was vibration levels. Single-cylinder four-stroke outboards normally vibrate more at or near WOT than when trolling due to the cyclical slowing down of the rev rate during exhaust and compression cycles. However, the Yamaha F6C outboard had higher mid-range vibration levels than the DF6 but actually smoothed-out above 4000rpm, the first time I’ve ever experienced this with a single-cylinder four-stroke outboard. Perhaps the long steering tube and offset mounting of the powerhead have something to do with this, but at WOT the Yamaha F6C had only slightly higher vibration levels than the twin cylinder F9.9F!

Powerhead access is very good with the sump oil-dipstick, carbie and spark plugs easily reached. The warranty coverage is four years for recreational applications but although the F6C has an OEDA "3 Star" rating the actual emission figures were not available during this evaluation.

 

YAMAHA F6CMHS SPECIFICATIONS

Engine type

Crossflow OHC four-stroke outboard motor

Cylinders/valves

1/2

Prop HP

6.0 at 5000rpm

WOT rpm range

4500-5500

Piston displacement

139cc

Bore x stroke

62mm x 46mm

Ignition system

CD w/electronic advance

Charging circuit

6amp w/o voltage regulation

Break-in period

10 hours

Fuel type

ULP 91 RON

Fuel

1.1lt integral/12lt remote

Oil type

SAE 10W30 Yamalube 4

Oil capacity

0.6lt sump

Gear ratio

2.08:1

Transom height

15in

Weight

27kg (dry)

Rec. retail price

$2391

Spare alloy propeller price

$73

Servicing costs*

Year one $299; Year two etc. $205

*As per manufacturer’s recommended schedule excluding parts. All prices current as of March 2010. Loan F6C from Yamaha Motor Australia, Wetherill Park, NSW, phone (02) 9757 0011. Prop and servicing prices from Coast To Coast Boating, Morisset, NSW, phone (02) 4970 5541.

 

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Originally published in TrailerBoat #258, June / July 2010

 


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