O
utboards sure have come
a long way since I started
long-term testing them in- The emphasis is now
on reducing environmental
impact. And judging by the amount
of low emission outboards sold in the
past year versus traditional carbie two-
strokes, the vast majority of boaters
obviously feel the same way.
According to the Outboard Engine
Distributors Association (OEDA), out of
the current unit sales of around 28,000
per year, 69 per cent or 19,300 of internal
combustion outboards sold are low
emission, whether four-stroke or DFI
two-stroke. Initially when I was shown
this figure I thought that would mainly
be higher output engines or those
115hp and above. But surprisingly even
with mid-range outboards there has
been a massive swing to low emission.
For example, from 41hp to 60hp the
low emission percentage is 92, while
amongst 61hp to 90hp engines the figure
is 95 per cent. From here upwards it’s
almost 100 per cent.
Although outboard sales are nowhere
near as high as pre-GFC when around
40,000 units were sold per year, the main
casualties have been carbie two-strokes.
Only amongst small outboards, those
under 10hp, do carbie two-strokes rule
because price is the deciding factor. A
far cry from its two-stroke emphasis
in the ’80s, Suzuki now offers carbie
two-strokes from 9.9hp to 40hp while
Mercury, Tohatsu and Yamaha still offer
a full range of carbie two-strokes up to
90hp. Until 2019 that is!
DFI TWO-STROKES
Currently only three manufacturers
offer this technology: BRP (Bombardier
Recreational Products) has Evinrude
E-TEC models from 15hp to 300hp,
Mercury 150hp to 250hp, and Tohatsu
30hp to 115hp.
E-TECs run single-stage injection,
where fuel is injected directly into the
combustion chamber like most EFI
car engines. Mercury and Tohatsu use
a two-stage system where air and fuel
are injected. These systems have the
distinct advantage for freshwater anglers
who do a lot of trolling, due to the
extremely lean air:fuel ratios resulting
from stratified combustion; and DFI
two-strokes use way less fuel at low rpm
than comparable output four-strokes.
However they still tend to idle rougher
than four-strokes.Both Mercury and Tohatsu are now
concentrating more on four-stroke
outboards, which is why Tohatsu doesn’t
offer a DFI or TLDI engine above 115hp,
whereas it sells four-strokes to 250hp
with 60hp and up being re-badged
Hondas. Most new boaters have the
belief that four-strokes are clean and
two-strokes are dirty, with DFI two-
strokes appealing more to long-term
two-stroke owners who simply want a
cleaner two-stroke without the inherent
complication and potentially higher
servicing costs of four-strokes.
To help boost sales Telwater (Quintrex,
Savage and Stacer) has taken over
packaging E-TEC engines with its boats,
so the line between packaged rigs and
loose units (those sold individually)
is a bit blurred. But there’s no doubt
packaging rigs does get more DFI two-
strokes into the outboard market.FOUR-STROKES
All outboard manufacturers offer
four-strokes in their product mix. BRP
re-badges Tohatsus to 15hp as does
Mercury to 30hp. Of course, Honda is
all four-stroke and Suzuki and Yamaha
are actively promoting four-strokes over
two-strokes.
Since the late ’90s when four-
stroke technology started improving
exponentially, lower emissions and
less weight have been the main thrust.
Manufacturers are putting way more
effort into developing four-strokes than
they ever did with carbie two-strokes.ELECTRONIC FUEL
INJECTION
Through the early and mid-’90s
when mid-range four-strokes started
appearing, most were afflicted with
multi carbies to achieve performance
not possible with single carbies. Trouble
was that unlike two-strokes where a
slightly out of tune carbie didn’t affect
performance much, multi carbie
four-strokes required careful balancing
of carbies to maintain engine tune.
Vacuum gauges were needed resulting
in a fiddly job. And due to slop in the
linkages between the carbies they went
out of balance fairly quickly.
EFI changed all of this by offering
true turnkey starting like a car engine.
It also enabled diagnostic computers
to be connected to determine engine
running faults. Honda led the field in
placing oxygen sensors in the exhausts
that sensed when a denser, higher
tradeboats.com.au 33