FORESTRYJOURNAL.CO.UK AUGUST 20 19 65Looking around the rest of the saw, it is all pretty
straight-forward. It’s when we get to the back and start
looking for the on/off switch and the choke lever that
things really begin to change; there is no choke and
there’s no on/off switch. But there is a primer button. I
have railed against primer buttons for many years. I have
never used them on the professional saws they are fitted
to and I’ve never really understood why they were there.
It’s a general rule of thumb that you don’t need a primer
button with a choke flap fitted in the carburettor unless it’s
on an amateur saw and the user needs all the help they
can get to start it.
So, in an attempt to reconcile myself with the stop
button and primer bulb lurking where the choke and on/
off lever would be on a conventional Stihl, I needed
to do some research about fuel injection.
I’ve looked at all sorts of fuel injection
systems, including the magnificent
two-stroke Detroit diesel once fitted in
many American trucks and one very
memorable Timberjack skidder the
FC ran out of Dalby workshops many
years ago. It’s a two-stroke with diesel
fuel, exhaust and inlet valves opened
and closed by a single camshaft that
also operates mechanical fuel injectors.
Each injector is a little self-contained
pump that squirts a dollop of fuel into
the cylinder at the right moment. There’s no
injector pump. It’s all done right there in the
cam cover with a low-pressure fuel supply to each
injector. The whole thing makes an unholy racket and
produces prodigious torque once it’s spinning at peak
rpm. It also produces enough pollutants to give the green
lobby a fit by the time it gets to the end of the street.
The Detroit doesn’t need much in the way of head
pressure to the injectors. Most injection systems need
some kind of pressure to get the ball rolling, though with
common-rail diesels it’s a whole other story we won’t get
into here.
The reason for the primer bubble is to provide a slightly
pressurised head of fuel in the system right through to
the fuel tank return. In most fuel-injected engines, and
on motorbikes in particular, you will hear an annoying
buzzing when the ignition is switched on. This is the
fuel primer pump providing head pressure for the fuel-
injection system. It isn’t practical to put a priming pump
and battery into a chainsaw (not yet, at least), so it’s down
to the operator and the primer bubble on the 500i is there
for that very good reason.
That covers almost all the technical stuff, except for the
remarkable power output of 6.8 bhp (5 kW), up from the
462’s substantial 5.9 bhp (4.4 kW) and its power-to-weight
ratio of 1.2 kg/kW against the 462’s 1.4 kg/kW and the
thing you can’t measure, which is sheer feel.
The 500i is light for such a powerful saw. It weighs
6.2 kg compared to the 6 kg 462 (both powerhead only,
with no fuel or oil) and that despite it being almost 1 0
per cent bigger at 79.2 cc, compared to the 462’s 72.2
cc. In practice, the 462 and 500i feel almost identical to
use, apart from the 500i feeling more powerful and
having notably rapid acceleration.
These are the things you notice most
about the 500i. Once you get past
pumping the primer bubble a few
times and tugging on the starter, the
reward is instant. There’s no uncertain
fuelling here. It revs clean and crisp
right from the start. Good practice
is to warm any saw through before
starting work and, given any new saw
in this class is going to cost around
£1,000, it’s essential to give them a
minute to warm through.
The 500i revs like nothing else out there
at the moment. Compared to the old 66 cc saws
we used back in the day, it’s almost unimaginable
how pedestrian it makes them feel. It accelerates in
an instant, with the quickest pickup I can think of on
any production saw I’ve tested, and it is a pleasure to use.
It makes cutting dry ash less of a task, and the added
benefit is that we fell and dress out big trees with one saw.
I ran the test saw on a 20” bar which is what we use
as standard for hardwood felling. I have tried it with a
25” bar fitted and it comes in handy for the bigger trees
in the stand, but it’s less handy when there’s a lot of big
branches to remove. The 500i doesn’t feel out of balance
with the longer bar and it certainly has no problems
turning it. You can bury the whole bar in a big tree and it
doesn’t back off, testament to the fuelling and the design
in general. This really is one exceptional saw that marks
the beginning of a new chapter in professional chainsaws.IT ACCELERATES IN AN
INSTANT, WITH THE QUICKEST
PICKUP I CAN THINK OF ON
ANY PRODUCTION SAW
I’VE TESTED, AND IS A
PLEASURE TO USE.
Above left: There’s no
carburettor anywhere to
be seen. It must all be
done by magic (or clever
electronics, anyway).Above right: No on/
off choke lever here.
There’s just an off
button and unless it’s
pressed, it’s on go.