Suzuki DF2.5

Released on the Australian market in January this year, the DF2.5 is the smallest and lightest four-stroke outboard Suzuki Marine has released. Weighing just 13kg, the DF2.5 has a 68cc single-cylinder OHV powerhead with thermostatically-controlled watercooling.

Developing 2.4hp at 5500 revs (based on 1hp equaling 746W) with a Wide Open Throttle operating range of 5250 to 5750rpm, the DF2.5 has a forward-neutral gearshift, 360-degree steering, twist-grip throttle control, four easily-adjusted trim positions and an automatically-engaging full tilt lock. Sensibly, Suzuki has incorporated a stopper device that prevents the powerhead rotating more than a few degrees when the outboard is fully tilted. Effective steering and throttle friction adjusters are provided.

Unlike its Honda BF2D competition, the DF2.5 has a moulded carry handle on the aft end of the lower cowl, ensuring the outboard will always be carried the correct way to prevent sump oil from flooding the cylinder. Alternatively, the outboard may be stored on its side on the moulded lower cowl lugs provided. The only apparent design fault is that, like the Honda, the upper cowl can not be removed completely from the powerhead due to the starter handle cord passing through a small diameter hole in the upper cowl.

Like the Honda, the DF2.5 has an easily-read oil level sight glass in the lower cowl, with the sump accessed by unscrewing a plug to one side of the sump, which holds 0.38lt of oil. But, unlike the Honda, which relies on splash or 'mist' lubrication and can only use Honda SAE 10W30 oil that's rated to a maximum ambient temperature of 32 degrees, the pressure-lubricated DF2.5 can use oils from 10W30 up to 20W40. However the Quicksilver four-cycle watercooled 10W30 oil used by my local Suzuki dealer can be used in all ambient temperatures from minus 20 degrees to over 40 degrees and provides rapid crankshaft, piston ring and rocker gear lubrication on cold starting.

Servicing intervals for the DF2.5 are every 50 hours or six months after the initial check-up at 20 hours. The waterpump impeller should be checked and/or replaced every 100 hours or once a year. A nice touch is the chrome rocker cover, which allows for valve clearance adjustment by removing four bolts, whereas this adjustment in the Honda necessitates removing the entire air cooling shroud, including the overhead recoil starter.

The DF2.5's large-capacity zinc anode just above the anti-ventilation plate should handle any leg electrolysis when the tender is rafted up alongside a yacht or cruiser.

ON THE WATER
Compared to the BF2D, the DF2.5 swings a relatively coarse-pitch prop for such a small outboard, even allowing for its 2.15:1 reduction ratio. But whereas the Honda has a 2.42:1 gear reduction and a 4.5-inch pitch prop compared to 5.4 inches for the Suzuki, the latter's prop is weedless and able to 'slip' a lot more under load compared to the Honda's 'high thrust' prop. The swept-back weedless blades also catch less weed than the Honda's prop.

The DF2.5 normally starts first pull, hot or cold, and reaches normal operating temperature in about two minutes from cold. The lack of water spraying from the exhaust relief holes until the thermostat has opened is a bit disconcerting and Suzuki should fit a separate pilot water discharge similar to the DF4 to DF6 range of four strokes.

Because of its small displacement powerhead, the DF2.5 idles in neutral at around 2000rpm and 1500 in gear, whereas with its centrifugal clutch the Honda idles at about 1500 in neutral. But, when trolling, the loan Suzuki would run for up to 10 hours on a litre of fuel compared to eight for the Honda. And, despite its 19 per cent greater piston displacement, the DF2.5 has lower vibration levels and, being watercooled, it is significantly quieter across the entire rev range.

Mounted on a Walker Bay 10 rowing and sailing dinghy to compare it directly with a BF2D two years earlier, the DF2.5 pushed the slippery displacement hull with incredible ease. Pushing a total of 270kg, including two adults, it averaged 4.3kts and hull speed at one-quarter throttle and 4.8kts at one-third throttle.

At half-throttle, it averaged 5.5kts compared to 4.9 for the same throttle opening with the Honda but, as the hull was squatting badly at this speed, there was little point in opening the throttle further.

In any case, the hull load at one-third throttle was sufficient to open the thermostat - essential with all marine seawater-cooled four strokes to prevent sump oil 'sludging', which can occur on prolonged low-load operation.

Best of all was the fuel efficiency. Over a loop, it averaged three knots with the throttle opening limited to half, with the DF2.5 using 0.23lt/h compared to 0.33 for the Honda across the same loop.

This incredibly low fuel consumption allows for more than four hours of cruising from the one-litre integral fuel tank compared to three hours for the BF2D.

WORTH THE EXTRA
At less than $1200, the DF2.5 retails for about the same as the BF2D and about $300 more than the two-stroke Suzuki DT2.2, which provides nowhere near the torque of its four-stroke counterpart. Frankly, when such fine outboard engineering is available for such a little extra (okay, valve clearance adjustment is really a dealer task and increases servicing costs) I see no point in buying a small single-cylinder two-stroke outboard. Having tested these kinds of engines for three decades, I can tell you that with the DF2.5 there's no comparison for fuel efficiency, torque and user-friendliness – not the least being the absence of oil smell in a following wind!

For more details on the DF2.5, phone Vanessa Norris at The Haines Group on (07) 3271 4400, or email vnorris@thehainesgroup.com