torquing
talk
WITH ANDREW NORTONEvolution of the Species
TOHATSU’S MFS6C HAS CERTAINLY EVOLVED FROM ITS 6A
PREDECESSOR, REPORTS ANDREW “ENGINE MAN” NORTONR
eleased in 2000
and also sold
as the Mariner
/ Mercury F6,
Tohatsu’s 123cc
MFS6A was the first single-
cylinder four-stroke six in
Australia. It was followed by
Suzuki’s DF6 in late 2002,
and Yamaha’s F6C in late
2009.
All three engines were
designed to provide low-
emission operation while
remaining relatively light.
They all have single-
cylinder OHV engines, with
the main diff erences being
piston displacement. All
have pressure lubrication,
CD ignition with electronic
timing advance, and the
option of integral or remote
fuel tanks, or both.THE NITTY GRITTY
The Tohatsu MFS6C,
released mid-2011, is the
first of these engines to
have an upfront gearshift
and a much longer tiller
arm. There are still six trimpositions with a single
shallow-water setting and
an automatic full-tilt lock
and reverse lock. The upper
cowl is more rounded than
the 6A, with an improved
air intake flow.
As with its predecessor,
only a 12lt remote fuel tank
is available.
A 12V, 5A unregulated
alternator is optional. The
engine still develops 5.9hp
at 5500rpm, with a wide
open throttle (WOT) range of
5000-6000rpm and a 2.15:1
gear ratio. The dry weight is
25.6kg. Tohatsu still hasn’t
fitted a carry handle to the
aft end of the lower cowl,
so you need two hands to
carry it instead of just one
for the DF6 and F6C. This
is a real pain over longer
distances.ON THE WATER
In June the Aussie Tohatsu
distributor, Lakeside
Marine, provided me with
a new MFS6C for extended
evaluation on my 2003 SeaJay 3.4 Punt — the same hull
I’ve also tested the DF6 and
F6C on.
Over an initial two-week
test period the borrowed
MFS6C was carefully run in
before performance trials
commenced. It started
easily hot or cold because
the choke is crosslinked
with the throttle. That said,
on each cold start it blew
some oil smoke for the first
minute or so, just like the
6A model I borrowed in
2000.
Spinning the standard
8in-pitch, semi-weedless
alloy prop and carrying a
total of 290kg, including two
adults and fishing tackle,
the MFS6C did a very good
job of pushing the load.
Although trolling operation
was limited to no more than
10 minutes at a time (first
10 hours), it ticked over
steadily with little vibration
through the hull. At mid-
range rpm the vibration was
on par with the DF6 and
lower than the F6C, but at ornear WOT the vibration was
greater than the F6C.
The minimum planing
speed on this engine is
also my recommended
maximum cruising speed
(to prevent powerhead
damage), achieved at three-
quarters throttle.
Although the F6C was
quicker at WOT than the
MFS6C,
the Tohatsu outperformed
the DF6, most likely due to
the fitting of a prop where
the pitch is greater than the
diameter. All props used
on planing hulls should
be designed this way in
order to achieve maximum
effi ciency — the DF6’s prop
loses effi ciency due to its
diameter being bigger than
its pitch.
Around a loop of normal
cruising including 10 per
cent WOT and 40 per cent
trolling operation, averaging
4kt (7.5kmh), the Tohatsu
used 0.52L/hr — 10 per
cent less than the DF6 (and
the F6C under identical78 tradeaboat.com.au