Yamaha 40X outboard motor review

The Yamaha 40X outboard motor had electric start and power trim and tilt when it was released in 1999. However, it also had an overhead recoil starter to tempt owners to try out their strength when firing up the big twin.

A manual-only start version of the Yamaha 40X is also available, and preferred by Pacific Islanders bristling with muscles. Known as the Yamaha E40X or Enduro 40 (pictured), it’s incredibly popular on everything from longboats to dugout canoes. This runs on a 50:1 premix instead of 100:1 for the Yamaha 40X.

Both versions have the largest piston displacement of any twin-cylinder carbie two-stroke outboard motor available. In many ways they’re a throwback to the big loopcharged twins of the seventies and eighties, such as the Johnson 40 to 55, Suzuki DT50 and Tohatsu 55, but have only one carbie to simplify maintenance and servicing costs.

The only other big twin to have a single carbie and power trim and tilt is the Mercury 40ELPTO that also has oil injection. But sensibly Mercury omitted the manual recoil starter to prevent owners from doing their backs in when showing off to female passengers.

YAMAHA E40X

Part of Yamaha’s CV (Customer Value) two-stroke engine premix carbie range from 25 to 50hp, the OEDA 1-star Yamaha 40X develops 39.4 brake horsepower (746 Watts per BHP) or 40 PS (metric HP at 735.5 Watts per MHP). Whichever power measurement you prefer, the engine develops maximum power at only 5000rpm.

Like the CV 25B and 30H, the Yamaha 40X has a rounded upper cowl that’s way more current in shape than the angular CV 50H which has a real eighties look about it, as do Yamaha’s three-cylinder two-stroke engine range from 30 to 90hp. But underneath that shapely cowl are some traditional outboard engineering, such as an electrically-operated manual choke and mechanical ignition timing advance. The alternator produces up to 6.7amp but lacks voltage regulation, so at least a 70amp/h start battery must be used to prevent “frying” it on long runs to and from a favourite fishing spot.

A nice touch is the auxiliary cooling water intake beneath the antiventilation plate; to provide some flow should the main intakes be clogged with weed. The main intakes are mounted well forward to deliver cooling water even when the outboard is trimmed well at WOT or tilted up for skinny-water access. The gear ratio is a usefully low 2:1.

Powerhead access is excellent, with the spark plugs, ignition timing linkages and bowl-type fuel filter easily reached. Like all Yamaha’s carbie premix two-stroke outboards the break-in period is ten hours where a 25:1 fuel/oil ratio must be used. The 40X is designed to run on standard unleaded (91 RON) but if premium (95) is used, then so must a semi-synthetic oil in order to stay in suspension with the petrol.

Yamaha recommends servicing the 40X every 100 hours or annually after the initial 20-hour check.

ON THE WATER

Mounted on a Stessl 4.4 Striker aluminium runabout the demo Yamaha 40X was badly under-propped swinging a 12in pitch alloy prop for our 620kg total including three adults. Another inch or two would have made a huge difference. Trolling at 700rpm my flab sure got a workout but by 1000rpm it had settled down, as had my blurred vision. Definitely not an engine to troll with!

Through tight turns at 4000rpm there was no prop ventilation but above this rpm the usual carbie two-stroke roar gave my tinnitus a workout out to 5700rpm where the rev limiter cut in.

THE VERDICT

For saltwater drift or anchor fishing the Yamaha 40X is an excellent repower engine for older aluminium runabouts like the Quintrex 4.3 Fishabout or 4.6m deHavilland Offshore. Both of these fishing boats were originally rated to 55 flywheel bhp or 49.5bhp at the prop.

At only 81kg the Yamaha 40X won’t damage the transom of these and should remain cheap to maintain and service for the life of the engine. And as it averages around 5lt/h for a mix of cruising and WOT runs, it will give a reasonable cruising range from the standard 24l remote plastic fuel tank, while the 100:1 fuel/oil ratio will reduce oil costs. Like all Yamaha outboards it has excellent saltwater corrosion resistance.

Parts for the Yamaha 40X are reasonably priced with a spare alloy prop, for example, costing only $180.

For more information, visit yamaha-motor.co.nz.

YAMAHA 40X SEA TRIALS

Average of two-way runs on Lake Macquarie, NSW, calm water.

RPM	SPEED (KTS)	FUEL BURN (LT/H)
700 (blurred vision)	2.5	1.5
1000 (could see again)	3.5	2.2
3500 (planing)	12.1	8.1
4000 (cruise)	15.3	8.7
5700 (WOT)	24.3	20.1

COMPETING OUTBOARDS

ENGINE	Mercury 40ELPTO outboard motor
Mercury 40ELPTO price	$AUS 6200
WEIGHT	80kg
BHP/RPM	39.9/4750
DISPLACEMENT	644cc
WARRANTY (YEARS)	5
OEDA STARS	1