REVIEW: SUZUKI DF2.5

When Suzuki released its DF2.5 in 2006, it didn’t do things by halves. Designed for small inflatables and displacement dinghies having transoms of no higher than 15in, the DF2.5 was light years ahead of its two-stroke competition yet weighed very little more.

FEATURES

Suzuki stuck with the proven concept of a gear-driven camshaft with push rods to the overhead valves. Unlike comparable output two-strokes, a one-piece crankshaft was used with capped connecting rods, just like the US-built two-strokes used to have. Because the fuel tank was mounted ahead of the crankcase the rocker cover was easily removable to check valve clearance, with the only disadvantage being the cowl couldn’t be completely removed from the engine pan due to the recoil starter cord passing through it.

As the power head is angled to port there’s plenty of space for the carbie to be mounted alongside the cylinder block and head instead of atop it. This reduces vapour lock on hot days after the engine has been stopped for a while then restarted. The 1lt fuel tank gravity feeds to the carbie which has a choke flap cross-linked with the throttle. Cold starting is simply pulling out the choke knob, cranking the engine, then slowly pushing in the knob as the engine warms without touching the throttle. Suzuki has long done this with its carbie outboards and works a treat.

The 0.38lt oil sump is large enough to reduce oil dilution and sludging that occurs when the engine is used for a lot of trolling. Not that trolling is this engine’s strong point as the minimum trolling rpm is 1500 due to the engine having fixed ignition timing. This also limits the DF2.5 to standard (91) unleaded only, as premium (95) has too high an octane for this engine and may cause pre-ignition and piston crown damage.

But having pressure lubrication ensures a wide variety of oil viscosities can be used. After the success of this oil in retaining its lubricating properties in my 2003 Suzuki DF6, Quicksilver FCW (four-cycle, watercooled) SAE 10W30 oil was used in the loan DF2.5 since new and has proven just as long-lasting between changes.

Four trim positions are fitted with a stopper knob for full tilting plus steering and throttle friction adjusters. So nice compared to the slide controls of the DT2.2 and other two-strokes in this power range. The engine can be pivoted 1800 for full power astern using the automatic reverse lock fitted. Really, the only omission is a pilot water discharge or tell tale leaving operators to feel down the leg for water spraying from the exhaust relief holes. No worries about feeling for the spray in following seas though as it blows straight back aboard!

Servicing intervals are 100 hours or annually after the first 20 hours. Though replacing the waterpump impeller is really a dealer-servicing task, once the warranty had expired on the loan engine which I acquired after one year, my mate Richard Ardizzone was able to replace the impeller without any issues. The original impeller was hardly worn but we followed the adage “prevention is better than cure”. Comforting to know the job can be done relatively easily when touring remote regions.

PERFORMANCE

Tested on four very different hulls the DF2.5 performed way better than expected providing the correct prop was fitted. Because of transom immersion at low speeds creating excessive drag the DF2.5 was unsuited to my two small tinnies but performed beautifully on my 3.8m Fairlite Gull sailing dinghy and Richard’s Walker Bay 10 swinging the optional 4.5in semi-weedless prop.

Though due to partial prop aeration on the Gull which has a 16in transom, the DF2.5 did vibrate excessively at certain rpm, whereas with deeper prop immersion and a vibration absorbing polyethylene hull hardly any vibration was transmitted through the Walker Bay 10. On the Walker Bay the DF2.5 failed to reach its WOT rpm, but this is not an issue on displacement hulls where engine load diminishes rapidly when the throttle opening is reduced slightly.

Starting is normally first pull hot or cold and the engine warms quickly from cold and has that wonderful exhaust beat only found in single-cylinder four-strokes.

Oil consumption has been low, as expected of an engine having pressure lubrication which is more efficient than splash lubrication at directing oil where needed. Over the first 48 hours, averaging 0.4lt/h with 7.5 per cent WOTh operation the fuel/oil ratio was 630:1, but from 48 to 90.6 hours with the same fuel usage and WOT percentage it had leaned to an impressive 2590:1. The second impeller installed at 48 hours is still pumping plenty of water after a total of more than 120 hours.

Saltwater corrosion resistance has been a little disappointing with paint bubbling around the leg/lower unit join and surface rust on the driveshaft despite the engine being freshwater flushed after each saltwater run. Had the DF2.5 been made in Japan instead of Thailand this corrosion may not have occurred as mates who have Japanese-made Suzuki outboards haven’t had these issues, which have also afflicted my Thai-built DF6.

Richard and I have found the best way of reducing salt deposits from the cooling water passages is to run the engine in a 200lt drum in gear at fast idle in freshwater for at least 15 minutes. By doing this at no time has the engine overheated due to passage restriction.

THE WRAP

For boats having transoms of no higher than 15in the DF2.5 is unbeatable and has never let Richard or me down over the 12 years we’ve been testing it. It runs so sweetly that I wonder how boaters ever tolerated small two-stroke outboards for so long!

To find your nearest dealer Google Suzuki Marine, click on Find a Dealer and enter your details.

SUZUKI DF2.5 SPECS

Type: Single-cylinder OHV four-stroke outboard

Rated BHP/MHP*: 2.4/2.4 at 5500rpm

WOT rpm range: 5250 to 5750

Displacement: 68cc

Bore X stroke: 48mm x 38mm

Gear ratio: 2.15:1

Weight: 13kg dry

RRP: $1211

OEDA stars: 3

*Brake horsepower/metric horsepower

SEA TRIALS

Single DF2.5 on Walker Bay 10, 4.5in prop and 270kg displacement including two adults and gear. Average of two-way runs on Lake Macquarie, NSW, in calm water.

“Loop” of cruising with 10% WOT operation and averaging 4kts equals 0.45lt/h

Single DF2.5 on 3.8m Fairlite Gull sail dinghy, 4.5in prop and 310kg displacement including two adults and gear. Average of two-way runs on Lake Macquarie, NSW, in calm water.

“Loop” of cruising with 10% WOT operation and averaging 4kts equals 0.42lt/h

Note better overall fuel efficiency on longer waterline hull. More intensive testing was not undertaken due to the high vibration transmitted through this classic fibreglass hull.

Check out the full review in issue #501 of Trade-a-Boat magazine. Subscribe today for all the latest boat news, reviews and travel inspiration.