ENGINE REVIEW - YAMAHA 15F PORTABLE OUTBOARD

Hard to believe, but the Yamaha two-stroke portable outboard motor has been around almost 20 years. In fact, it uses the same base powerhead released in Australia way back in 1983.

But that’s a good thing because the old 15D and its Yamaha 15F successor have been some of the most popular outboards here. Though both are premix engines the fuel/oil mix is a lean 100:1 that reduces oil costs and pollution. Both have low vibration levels for loopcharged twins that are high enough to reduce tiller arm flab but not induce numbness after a long run to a favourite fishing spot.

The Yamaha 15F portable outboard motor also has an upfront gearshift and one of the cleverest cold-starting systems I’ve ever tested. It’s also marginally lighter than the 15D. Mind you, not as light as its main crossflow US two-stroke competition.

15hp Yamaha two-stroke

The Yamaha 15F portable outboard motor has a typical twin-cylinder, single-carbie Japanese loopcharged powerhead with a multi-section crankshaft and solid conrods, unlike its direct US competition that has traditional marine engineering of one-piece crankshaft and capped conrods, just like all four-stroke outboards currently available.

Where the Yamaha 15F portable outboard motor differs from its direct competition is the cold-start system. Instead of a fuel primer Yamaha opted for a cable-operated system of choke, ignition timing advance and throttle opening. Pull the choke knob to the first stop and the choke flap partially closes. Second stop and the mechanical ignition timing advances slightly. Third stop and the throttle opens slightly. Instant cold starting, no playing with the throttle opening and rapid engine warm-up.

A 12V 6.7amp lighting coil with attaching plug on the engine pan is standard, though a rectifier kit must be added to charge batteries. As there’s no voltage regulation I recommend at least a 60amp/h battery to prevent frying on long runs.

Powerhead access is very good, with the spark plugs and bowl-type fuel filter easily reached. Servicing intervals are every 100 hours or annually after the first 20 hours and a 25:1 break-in mix is needed for the first 10 hours. Either standard (91 RON) or premium (95) unleaded can be used, but only the latter with a semi-synthetic oil or fuel/oil separation may result. The warranty coverage is three years.

Performance

How lucky for me to have a Yamaha 15F portable outboard motor review test for almost eight years, commencing way back in April 1996. I had the time to carefully run-in the engine and test it on my 1988 3.6m Sea Al Super Skua tinny, which went to a collector in Sydney two years ago.

Run at all times on 91 RON unleaded and Yamalube 2 (thoughtfully supplied by Yamaha Motor Australia) the 15F provided countless hours of angling pleasure, mostly with my vegetarian partner Susan who tolerated my pedantic nature for 12 long years. We voyaged all around Lake Macquarie, exploring nooks and crannies using my ’97 Mariner T2400 trolling motor mounted to starboard (it has a left-hand prop) of the Yammie for really slow trolling.

The standard 10.5in pitch alloy prop matched the 2.08:1 gear ratio well on the Sea Al and the 15F outperformed all the direct two-stroke competition tested on this hull. It also returned way better fuel efficiency. Though it did tend to get a little raucous at wide open throttle, overall it was quiet for a two-stroke 15 and my somewhat lesser flab back then still got a bit of a workout at trolling rpm. But not my tinnitus because the dry exhaust relief made for very quiet running.

The Trade-a-Boat verdict

Naughty me, I replaced only three new water pump impellers and one thermostat during the eight years, instead of one new impeller per year. After that time and despite saltwater-only use (though with a freshwater flush each time) there was absolutely no corrosion anywhere on the engine.

Carrying the Yamaha 15F portable outboard motor was fairly easy using the foldout handle in the transom brackets. Though, as I became weaker with age (too many heavy outboards when young), even this engine started to weigh too much to lug around. No problem selling the 15F as the first person who saw it bought it without quibbling over the asking price. And no portable outboards over 30kg nowadays.

Our Yamaha 15F portable outboard motor was reasonably cheap to operate and service yet had the grunt to get us quickly back to our boatshed when the lake turned nasty, even though sometimes we ended up looking like drowned rats by the time we got ashore. The 15F still remains my all-time favourite two-stroke 15.

The Yamaha 15F portable outboard review motor was supplied by Yamaha Motor Australia, Murrarie, QLD, phone (07) 3906 7000.

Yamaha 15F portable outboard sea trials

Single Yamaha 15F on 3.6m Sea Al Super Skua, total 295kg including two adults and fishing tackle, average of two-way runs over low chop

“Loop” of cruising with 10 per cent WOT operation and averaging 8kts, fuel flow 2.7lt/h and range over 50nm from standard 24lt plastic remote tank with 20 per cent reserve.

* Worse fuel efficiency due to larger throttle opening than when cruising. Note trolling efficiency with loopcharged powerhead.

Yamaha 15F specs

Yamaha 15F price: $2865 RRP

TYPE Twin-cylinder premix two-stroke portable outboard motor

RATED HP 14.7/15 at 5000

REC. RPM RANGE 4500 to 5500

DISPLACEMENT 246cc

BORE X STROKE 56 x 50mm

WEIGHT 36kg (dry, short shaft)

OEDA STARS 1

See the full version of this review in Trade-A-Boat #473, on sale December 2015.