If you're considering re-powering your small boat, why not spend a few extra dollars on a clean-technology 40hp outboard and enjoy the benefits of improved fuel economy, less noise and less pollution


Honda BF40
De-rated from its 50hp counterpart, the BF40 was originally released on the Aussie market in 1993 as the BF35 and was upgraded to a 40 three years later.

Standard features include low-oil-level/pressure and engine-overheat alerts (a loud beeping noise and automatic rev reduction), a rev limiter and lower unit speedo pickup. Electrically operated and manual chokes are fitted for simplicity and reliability. Electric-start models lose the overhead recoil starter.

Mounted on a Horizon 4400 aluminium runabout and spinning the standard 13in pitch alloy prop, the demo BF40 started instantly hot or cold, refused to blow any oil smoke and had very low vibration and noise levels across its entire rev range.

Pushing a total of 740kg including three adults and two kids, it trolled us at 5.4kmh on 800rpm using 0.8lt/h and cruised at 28.3kmh on 4000rpm using 5.5lt/h. However there was a fair amount of prop ventilation through tight figure-eight turns at these revs.

The wide-open-throttle (WOT) average was 47.4kmh on 5600rpm using 14.1lt/h, and powerhead access is very good.

Johnson/Suzuki 40
De-rated from their 50hp counterparts, the Johnson and Suzuki versions are identical apart from paint and decals. In my opinion they outperform their direct four-stroke competition, particularly for throttle responsiveness.

The sequential multipoint EFI enables the DF40 to deliver consistent operation regardless of barometric pressure (altitude) or ambient temperature.

Mounted on a Blue Fin 4.5 Weekender aluminium runabout, the demo DF40 was significantly under-propped for our load of two adults and gear, giving a total displacement of 700kg, but with a family of four aboard the engine would have been propped just right.

Just like an EFI car engine, the DF40 started instantly hot or cold and maintained a steady 900rpm in or out of gear. No oil smoke was apparent at any time, and across the rev range vibration was virtually non-existent, while the engine was quieter than comparable carburetted four-strokes.

Spinning a 13in alloy prop, the Suzuki trolled at 4.2kmh using 0.7lt/h and cruised at 25.8kmh on 4000rpm using 5.6lt/h. Through full-lock figure-eight turns at 5000rpm, there was no prop ventilation and the hydrodynamically efficient lower unit enabled the leg to be trimmed right out without prop blow-out occurring.

The WOT average was 48.4kmh on 6100 revs using 13.1lt/h.

Powerhead access is good. The integrated ignition coils and spark-plug leads eliminate radio "noise" and reduce powerhead clutter. The bowl-type fuel filter is easily checked for fuel contamination, but the oil filter is a little difficult to reach. A trim gauge should be standard equipment. 

Mariner/Mercury F40 and EFI 40
Up-rated from its 30hp counterpart, the F40 performs significantly better on similarly sized hulls and has a proven reputation for reliability.

Up until a couple of years ago the F40 was available as an electric-start power trim and tilt carburetted model, but now apart from the manual start 40ML, all models have standard single-point EFI, making them more appealing for anglers fishing alpine dams such as Eucumbene, and improving running qualities regardless of ambient temperature.

Manual-start versions have an automatic choke system and automatic decompression, where the exhaust valve stays slightly open until the engine reaches minimum cranking revs.

All models have rev limiters and low-oil-level/pressure and overheat warning systems, which reduce engine revs to a safe level. Electric start models lose the overhead manual recoil starter.

So far I have been unable to test the EFI F40, but on a Bermuda 410 Nautica aluminium runabout, the demo carburetted F40 started easily every time and never blew any oil smoke.

Spinning a 13in alloy prop and pushing a total of 570kg including two adults, the F40 trolled us 4.1kmh on 620rpm using 0.6lt/h with slightly higher vibration levels than a Honda BF40 (although the revs were 180 fewer) and cruised us quietly at 32.6kmh on 4000rpm using 5.6lt/h. Through tight figure-eight turns at these revs, no prop ventilation occurred.

The WOT average was an impressive 54.4kmh on 5650rpm using 12.8lt/h and the engine had lower noise levels than comparable three-cylinder two-strokes.

Although the wiring around the powerhead is a little untidy, access to the oil filter is good and the carbie linkages appear easy to adjust. Powerhead access on the EFI model is a little tighter but still reasonable. 

Yamaha F40B
Up-rated from its F30A counterpart, the F40B was released locally in 1999 to replace the F40A, which was a de-rated four-cylinder version of the F50A.

Standard features include a cold-start fuel primer that acts like an automatic choke system, low-oil-level/pressure and overheat alerts with automatic rev reduction, a rev limiter and automatic decompression and gas-assisted tilting in the manual-start model.

At the F40B's Aussie release, I tried both the manual and electric-start versions and the former started easily from cold with a firm two-hand tug on the overhead recoil starter, which unfortunately is omitted in electric-start models. The electric-start version started instantly hot or cold, and neither version blew any oil smoke.

Mounted on a Quintrex 455 Escape aluminium runabout and pushing a total of 750kg comprising three adults, the demo F40B provided adequate power. Spinning a 12in alloy prop it trolled at 4.8kmh on 750rpm using 0.7lt/h with slightly higher vibration levels than the demo Mercury F40, and cruised quietly at 29.8kmh on 4000rpm using 5.9lt/h.

The WOT average was 46.1kmh on 5800rpm using 13.5lt/h, and at these revs noise levels were comparable to the carburetted Merc F40.

Powerhead access is good, the oil filter is easily reached and overall the powerhead has a clean appearance. The first service is at 10 hours, when the valve clearance should be checked.


Evinrude E-TEC 40hp
De-rated from its 50hp counterpart, the E-TEC 40 is the only twin-cylinder outboard of the low-pollution 40s, giving it a very low profile.

The DFI system is completely self-contained and should the battery be flat the engine can be started manually. Other features include no belt drives anywhere on the engine; electronically controlled unit injectors, which pressurise the fuel to 550–700psi; and a massive output variable voltage alternator and Speed Adjusting Failsafe Electronics (SAFE), which reduce engine revs should the oil level in the under-cowl tank drop below a preset level or the engine overheat.

According to Bombardier, the fuel/oil ratio at dead slow troll is 360:1 - leaner than the 300:1 for Fichts. Based on Bombardier's belief that 60:1 is the optimum fuel-to-oil ratio for Fichts, the E-TEC system should be the same.

Briefly tested on a Blue Fin 4.2 "top-ender" style hull, the tiller-steer demo 40 started instantly hot or cold and didn't blow visible oil smoke.

Spinning a 17in stainless-steel prop and pushing an estimated 650kg total including two adults, two hefty deep-cycle batteries and a bowmount Minn Kota, the demo 40 trolled at 3.7kmh on 650 revs, achieved a clean plane and slow cruise at 23.3kmh on 3400rpm and averaged 47.7kmh on 5500rpm.

Bombardier was unable to supply fuel-flow equipment, but based on testing of an E-TEC 75, the 40 should consume around 0.5lt/h at 650 revs, 6.5 at 3400 and 13.4lt/h at WOT. At all revs the engine was very quiet for a 40.

Vibration levels were reasonable, but not as low as most three-cylinder four-strokes; nor was power delivery across the rev range as consistent as the Johnson/Suzuki DF40, with the usual Orbital and Ficht "flat spot" on transition from stratified to homogenous combustion.

To ensure gearcase oil longevity, the lower unit is straight from the Johnson 55 commercial outboard and swings large-diameter, coarse-pitch props, which create excessive prop-steer torque on planing hulls when the leg is trimmed right in. But then low-speed manoeuvrability is absolutely brilliant.

Tohatsu TLDI 40
De-rated from its 50hp counterpart, the TLDI 40 utilises the orbital combustion process, which functions by injecting air into the fuel-delivery rail at 80psi, which then mixes with fuel pressurised to 90psi and directed to the three combustion-chamber injectors.

This results in complete air/fuel atomisation (down to a fuel droplet size of only five microns) without having to resort to high fuel-injection pressures.

A single throttle body air intake incorporates throttle position sensors for load and barometric pressure (to ascertain the correct air/fuel ratio). According to Tohatsu, the multipoint oil-injection system varies the fuel/oil ratio from 50:1 at WOT right down to 450:1 at idle, and an electric oil pump accurately delivers oil where it's needed.

The stratified combustion system below about 3000 revs gives an air/fuel ratio of about 40:1, richening to 25:1 when the engine operates on homogenous combustion. By way of comparison, an EFI four-stroke has an air/fuel ratio of about 14.5:1.

Standard are warning systems for engine over-rev (6000rpm), low oil, engine overheat and low battery voltage. Should any of these problems occur, after a pre-determined period the revs will be progressively reduced to 900.

The ECU has at least 300 hours of memory and records any operating problems encountered during this period, while 28 troubleshooting codes and various combinations of the three warning lights in the analogue tachometer allow a servicing technician to analyse problems without needing a laptop computer.

So far I have not tested the TLDI 40, but it should perform almost as well as the TLDI 50.

Powerhead access is good and the air-compressor drive belt, fuel pump, vapour separator, injector block and throttle body assembly are easily reached. First service is at 10 hours, but a battery of at least 80amp/h capacity must be used, as the management computer and electric oil pump draw a fair amount of current and voltage must be maintained above 10.8.

Having not yet tried the TLDI 40, I can't comment on how well it compares to the direct four-stroke competition.

But while the E-TEC 40 is the logical progression from the carburetted twin-cylinder two-stroke Johnson 40, it doesn't match the Johnson/Suzuki DF40 for low vibration levels, consistent power delivery and minimal prop torque steer. However, its excellent fuel economy and long servicing intervals put it in strong contention.

The Johnson/Suzuki DF40 is my choice of the low-pollution 40s. Haines Suzuki Marine has fitted one to a Clark 430 Navigator runabout for me to conduct extended evaluation on, and full test results are scheduled to appear in an upcoming issue of Trailer Boat.

All the engines listed comply with US EPA 2006 exhaust-emission regulations, but in addition to this the Honda BF40, Mariner/Mercury EFI F40, Johnson/Suzuki DF40 and Evinrude E-TEC 40 meet California Air Resources Board (CARB) 2008 requirements. The DF40 also meets EU2005 requirements, and the E-TEC 40 meets EU2006, which takes into account noise emissions.

Four-strokes produce fewer hydrocarbon (HC) emissions than DFI two-strokes, but higher levels of carbon monoxide (CO) and oxides of nitrogen (NOx).

Standard are two-year warranties for recreational usage apart from the E-TEC 40, which has three years. The Mariner/Mercury F40 and EFI F40 now have a standard three-year warranty.

Recommended servicing requirements for the four-strokes are every 50 hours (100 for the BF40) with waterpump impeller replacement every 100 hours. Apart from the Yamaha F40B, the first service is at 20 hours, when the valve clearances should be checked.

All the four-strokes have canister-type oil filters. The Tohatsu TLDI 40 requires servicing every 50 hours with impeller replacement every 100, while the E-TEC 40 doesn't require any servicing for the first 300 operating hours or three years.

40hp four-strokes
Engines: Honda 40 Johnson/Suzuki 40 Yamaha 40 M/M 40
Engine type: All engines crossflow three-cylinder
Valves: 6 12 6 6
Valve actuation: SOHC DOHC SOHC SOHC
Drive: Belt Chain Belt Belt
Prop hp @ rpm:  
Carburetted: 39.4/5700 - 40.1/5750 39.4/5500
EFI: - 39.4/5500 40.1/5750 -
Piston displacement: 808cc 814cc 747cc 747cc
Bore x stroke: 70 x 70mm 71 x 68.6mm 65 x 75mm 65 x 75mm
Ignition system:  
Carburetted: CD with electronic timing advance
EFI: Electronic engine management
Charging circuit (amps):  
Carburetted: 10 regulated - 6 unregulated 15 regulated
EFI: - 18 regulated 20 regulated -
Break-in period: 10 hours 10 hours 10 hours 10 hours
Fuel delivery:  
Carburetted: 3 single barrel - 3 single barrel 3 single barrel
EFI: - sequential singlepoint multipoint
Fuel type: All engines 91 RON ULP
Fuel capacity: 25lt 25lt 25lt 24lt
Oil type (SAE): 10W30/40 10W30/40 10W30/40 10W40
Oil capacity: 2.4 2.2 2.0 2.0
Gear ratios: 2.09:1 2.27:1 2.00:1 2.00:1
Transom height: 20in 20in 20in 20in
Weights (kg):  
Manual start:  
Carburettor: n/a n/a 91 84
EFI: - - - -
Electric start:  
Carburettor: 96* - - 91*
EFI: - 110* 101* -
RRP: $8272* $8325* $8999* $8272*
* Weights and prices are electric-start remote-control versions with power trim and tilt

40hp two-strokes
Engine: Evinrude E-TEC 40 Tohatsu TLDI 40
Engine type: Two-cylinder DFI Three-cylinder DFI
Prop hp @ rpm: 40.2/5000 39.4/5500
WOT rev range: 4500-5500 5150-5850
Piston displacement: 864cc 697cc
Bore x stroke: 91 x 66mm 68 x 64mm
Ignition system All engines feature electronic engine management
Charging circuit: 75 23
Fuel/air scavenging: Loopcharged Loopcharged
Fuel delivery: High-pressure single stage Low-pressure dual stage
Fuel type: 91 RON ULP 91 RON ULP
Fuel capacity: 22.7lt remote 25 remote
Oil type: Bombardier XD100 High Performance Valvoline TC-W3
Oil capacity: 1.9lt 2.0lt
Gear ratio: 2.67:1 1.85:1
Transom height: 20in 20in
Manual start: 104 -
Electric start: 109* 95.5*
RRP: $8309* $8576*
*Weights and prices are for electric-start remote-control versions with power trim and tilt

Published : Thursday, 1 July 2004

Prices and specifications supplied are for the market in Australia only and were correct at time of first publication. makes no warranty as to the accuracy of specifications or prices. Please check with manufacturer or local dealer for current pricing and specifications.

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