Talking Torque: Balancing Act

Andrew Norton — 13 June 2019

When pondering a manual start 40 it's essential to consider your ability to actually start the engine. Sure, some simple twin cylinder two-strokes are still available – such as the 696cc Suzuki DT40 and 703cc Yamaha Enduro 40 – but unless you've been bulking up, these engines are very hard to start when cold.

The trouble is that having two large displacement cylinders, even with one piston up and one down, creates an imbalance that requires a lot of effort to overcome. Add another cylinder, however, and the balance is restored to the extent that even a two-stroke outboard of over 800cc can be started manually without permanent back or shoulder injury. Yamaha's 849cc Enduro 60 is a prime example.

Therefore, starting a smaller displacement three cylinder outboard, such as the Mercury 40LW (40 Super, as it's recently been re-named) is no sweat. Since 2001 I've tested three of these and each has started cold with a firm two-hand pull and only one hand is needed when hot.

The only real complexity with this engine is that it has three carbies, whereas the DT40 and Enduro have one. But providing the carbie linkages are kept well lubricated the engine should hold its tune between services. In any case, because of the way lower compression ratios in two-strokes compared to four-strokes having three carbies slightly out of tune won't adversely affect performance, whereas in four-strokes the engine will run like a dog.

Being de-rated from 50 HP the 40 Super is a very under stressed engine. It can even cope with slight over propping as I found out when testing my first 40 Super.

The nitty gritty

The Japanese-made 40 Super has the same cylinder bore as its twin cylinder 30LW counterpart with a slightly longer piston stroke. The ignition timing advance is mechanical and the chokes are manually operated via linkages, as are the throttle opening flaps for the carbies. The optional 12 volt, 130 watt alternator has voltage regulation so it won't fry a battery used for electronics on long runs to and from favourite fishing spots.

Power head access is excellent with an easily-reached bowl type fuel filter and spark plugs. The break-in period is ten hours on 25:1 before switching to the normal 50:1 ratio. Providing a semi-synthetic oil is used, the engine can be run on either standard (91 RON) or premium (95) unleaded. Although engine performance won't be enhanced by using 95 the possibility of using fuel tainted with ethanol will be reduced.

Six trim positions allow for fine tuning of leg angle relative to transom rake (I've found the third position seems the best all rounder) and a single shallow-water drive setting is provided, along with a full tilt lock.

Servicing intervals are every 100 running hours or annually after the first 20 hours/three months and provided the 40 Super is serviced by an authorised Mercury Marine service centre the total warranty coverage is five years.

On the water

The first 40 Super was mounted on a 4.45 metre Sea Jay Escape 'top ender' style of tinny and though over propped provided reasonable performance at or near Wide Open Throttle with excellent midrange fuel efficiency. On this hull the demo engine was a bit chuggy below 1,000rpm but quickly smoothed out above this, and out to WOT very little vibration was transmitted through the tiller arm. Like all carbie two-strokes it became a bit raucous at WOT but when throttled back was reasonably quiet. Despite being on a hull with a long deep keel and swinging an alloy prop, no prop ventilation occurred through tight figure of eight turns at 4,000rpm.

Next up was a 4.8 metre Kiwi-built Smartwave 4800 polyethylene open dinghy and this time opting for the standard prop made a world of difference, with the engine being slightly under propped and handling the significantly greater hull displacement much better. All Japanese outboards love to rev and slight under propping on planing hulls is always the way to go, especially when pushing heavier loads.

Most recently was a 4.1 metre Brooker open tinny. I'd tried this hull in the past with 30 horsepower outboards and the additional power transformed this hull into a sprint boat. We didn't have time to do performance trials since we were using it as a camera boat while photographing a Force Crossover 26, a review that appeared in Trade -a-Boat issue 478. Being used to simple things in life I think I actually enjoyed driving the Brooker more than the Force 26. The guys who supplied the Brooker couldn't believe I started the engine manually instead of using the electric starter but as the 40 Super is such an easy engine to start I couldn't resist.

The only drawback of the 40 Super is its side gear shift, an upfront shift would make the engine nicer to use.

All three engines were well finished with excellent paintwork as expected of a Mercury product.

The wrap

This year there has been a mad rush by commercial operators to buy carbie two-strokes before the ban on buying new outboards comes into force in next year. One outboard importer told me that a local hire boat company ordered 26 outboards to ensure it would still have lightweight engines long after the ban came into force. 

According to OEDA 92 per cent of all outboards sold in Australia last year in the 40 to 60 horsepower market were low emission engines, whether four-stroke or DFI two-stroke. So is there a point in buying a 40 Super when down the track its resale will be nowhere near as high as a comparable output four-stroke?

The decision should be based on what type of hull it will be mounted on and how frequently the engine will be used. If you're re-powering an older tinny, such as a Quintrex 4.3 metre Seaman, which was never designed to take the weight of a four-stroke 40, then the 40 Super makes great sense as the additional weight will damage the hull and in any case over capitalising on an older boat is illogical (I've been caught out this way). However, if your hull can take the weight and you can afford the additional purchase and servicing costs then a four-stroke 40 would be the answer.

At the moment Aussie boaters have a choice of whether to go carbie two-stroke or low emission. But as outboard manufacturers expect to close off forward stock ordering by June this year it will be increasingly hard to buy a new carbie two-stroke outboard as existing stocks dwindle. That will just be another example of the nanny state in which we live where choices are taken from us without asking if we agree or not. At least our mates across The Ditch still have choices!

For your nearest dealer Google Mercury Outboards Australia, click on Find a Dealer then enter your postcode.


Mercury 40 Super

Engine type Loop charged 3 cylinder two-stroke outboard

Rated BHP/MHP* 39.9/40.5 at 5350rpm

WOT rpm range 5000 to 5700rpm

Displacement 697cc

Bore x stroke 68 × 64mm

Gear ratio 1.85:1

Weight – long shaft only 72kg

RRP $4,940

OEDA stars 1 

*Brake horsepower/metric horsepower or PS.


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Andrew Norton