Derestriction
and tuning
of 50cc scooters
Most world markets require that 50cc scooters are
supplied in restricted form to comply with local
licence
requirements for young riders. Of course
once a rider is of an age and has the right type of
licence, there's nothing
to stop them derestricting
their scooter to enjoy a little more performance.
That's one way of extending The 'snelf-life' of your
scooter investment. Most mooerr scooters have
the
looks to outpace most sports cars in the car
park grand prix, but the reaiity out on the road is a
little different.
They might hang tough on the street
Dut simply don't nave me power to pack up their
aggressive looks, Acceleration s not a problem for
most small capacity scooters out tneir lowly top
speeds
are reached all too guickly It can get
frustrating riding everywhere at SOmph flat out
especially wnen your scooter has oeen designed
with handling and brakes that can easily cope with
much
higher top speeds,
But all is not lost. Basic oerestnction is a
relatively straightforward procedure on most
models and
it's ppssible to unleash a top speed of
between 45 and 50mph without creaking the
bank, sometimes without spending any money
at all,
Beyond basic derestnct'on there is a huge pool
of attprmar^pt si inpiliprs ann ti inino ^oPnia'i^tc; tnat
can supply go-faster goodies ana the technical
expertise to make the most ot your scooter's
potential,
And that potential can be realised
whether your goal is simply to bea: your mates
round the streets or mix it with the
fast folks on
the racetrack,
Just remember the basic rule of tuning -
there's always a trade-ott, Whether that means a
less civilised,
smooth and tractable ride, poorer
fuel economy or compromised reliability depends
on how far you take things. For example a race-
tuned
scooter on urban streets would be a misery,
as all the power is usually at the top end and
raised gearing will tend
to compromise
acceleration at me expense ot me rrgner speeo
needed for racetracK work, And once you've
spent a few
hours razzing a full-nouse race motor
on the street it'll be t'me to get stuck into the
considerable Time, not to mention expense, of
rebuilding it,
The trick with tuning is to have all of the
elements working together to deliver the type of
usable
performance you want, The good news is
that there's enough headroom even on standard
scoots to raise performance safely
and reliably.
The scooter
The machine shown be'ow is an aging 1993
Yamaha B Whizz, but nonetheless provides a
OCiCiQ i?Y3mpl(? o.t \,',/nat can bp oonp This c; thp
scoot that was at tne vanguard of the current
sports scooter craze, and was first introduced
over ten
years ago, Although it's now looking a
bit dated, it's stili a current model in some
countries, and the engine and transmission
are
still in use on loads of scooters worldwide, so
it's a good example to use to show wnat's
available to pep it,
and countless scooters iiko
it, up
Beyond basic derestnct'on there is a huge pool
What does what
Any tuning modification1 you mate to your
scooter's engine has an effect on the
transmission. So lets miina ourselves of how ;ne
transmission worKS fo1 fuily understand what
Happens
as we go in pursuit of speed
There are four basic elements.
1 The front pulley
The front pulley is two separate plates forming a
V in whicn the drive belt sits. At low revs the
pulleys
are wide apart so the belt sits further down
in the V - this gives a iow starting gear so the bike
can pull away. As
She revs rise, centrifugal force
pushes the halves of the V together, forcing the
beli 10 [tie outside and giving a
higher gear for
better top soood
2 The rear pulley
This behaves in exactly the same way as the front
puiley, but in reverse - low revs mean the halves
of
the V are kept together for low
gearing/acceleration, and higher revs force them
apart for Higher gearing/top speed.
Because the
two pulleys behave oppositely, the belt is
automatically kept at the proper tension.
3 The variator
Th\s works in tandem with the front pulley. The
pulleys control the range of gearing, but the
variator
controls the RATE at which the gearing
changes, It does this with weights that are thrown
outwards by centrifugal force
up ramps in the
variator, in the process forcing the two pulleys
together. The heavier the weights, the quicker the
gearing
rises, the lighter the weights, the longer
the gearing takes to raise itself. So if you have an
engine with lots of
midrange, you can raise the
gearing sooner because it will still drive, so you
use heavier weights. If you have a peaky
engine,
you want to keep the gearing down for longer to
allow the engine to get up into its power band, so
you use
lighter weights. Many manufacturers
crudely but effectively restrict the top speed of
their machines by having a plate
bolted
concentrically to the variator which prevents the
weights from being thrown fully outwards, hence
keeping
the gearing low,
4 The clutch
This covers the transition from ticking over and not
moving, to actua'ly driving along. A steel drum
driven
from the rear pulley spins round a set of
clutch shoes (like a drum brake's shoes) that are
pivoted at one end and sprung
at the other. At
tickover the centrifugal force isn't strong enough to
move the shoes against the springs, but as the
revs
rise the shoes are thrown outwards against
the drum, You can change the springs to vary the
point in the rev range at
which the clutch
engages, or you can change the whole clutch for
an adjustable one, which can be varied to deal
with
different conditions and types of riding.
This is the most copula'- modification for three
reasons. Firstly, tno mai" restr'ction for most
scoots
s in the exhaust. There's often a washer 'y
a o'\oe welded into the neader end that can oe
extracted
with the caret'u apDi.icafon of a Dren'e
or similar type of tool to grind away the weld
holding in tne restrictor.
A step up from simole derestoction of tne stock
o\oe is changing it for an aftermarket performance
item.
But be aware toat some of these are not for
roaa or highway use, so you may fail foul of the
iaw if stopped at the roadside.
But fitting the right
performance pipe can have a huge effect. They
can also look very good and trick and are usually
a
cinch to fit
'st Dices don't need changes to the
carburettor settings, however check with your
nearest runing shop
to bo oure. But many do
come witn different weignts for the variator which
can be tncky to set uo nght, so if you're
not
confident n your mechanical caoabilities, get an
expert to oo if. This is a Ninja Super Scoot pipe,
cheapest of aftermarKet exhausts, but it fits
straight on, gives a healthy power increase, and
has a
nice deep tone - many aftermarket pipes
sound liKe a couple of wasps in a bean tin, so that
while you might have been
frustrated at your
scooter's lack of go, the whole neighbourhood is
now irritated by your rasping attempts to screw
every
last gram of oower out of your bike.
VARIATOR
You don't strictly need to change this, as you can
just change the rollers in the standard item after
removing
any restrictor plate as described earlier,
but a racing variator gives you a smoother and
more accurate change in ratios
as the revs rise.
Fitting one is not difficult, but you may need a
special tool to hold the pulley while you undo the
nut.
The B Whizz was fitted with an Omega
Racing Concept variator, which comes with three
sets of weights to fine tune the
response to suit
your other modifications
CLUTCH
Depending on the level of tune, your scoot might
benefit from different clutch springs or even an
adjustable
clutch. This allows you to choose
exactly where the clutch bites, so if you've got a
very peaky, powerful engine, you'll
adjust it to
come in at higher revs to give the engine a
chance to spin up nicely.
DRIVE BELT
Opinion is divided on whether the standard belt's
up to the job with a tuned engine. It's best not to
taks
any chances in this department to avoid
being stranded at the roadside it tne standard belt
lets go. And there's a possibii'ty
of a more
frequent irritation in the form of a constantly
slipping belt under the new improved load
generated by
your derestricted/tuned sooot, There
is a variety of belts available made from super
strong and durable Kevlar. Tne
one above is by
tuning parts specialist Malossi
REAR SHOCK
The B Whizz is not alone in having a very basic
rear shock absorber, The rear suspension unit's
often
one of the first victims when manufacture''s
are looking to build scooters down a orice This
Top Performance shock is
anything but basic - ,t
has an anodised aluminium body and adjustable
spring preload and damping. This type of shock
can
be adjusted to suit the type of riding you do,
whether it's hard soio blasts or two-up riding with
a passenger, or even
carrying luggage on a
camping trip.
The standard carburettor is often tuned lor the
scoot's restricted status, so substituting it with a
larger
bore item can help to boost tho power. The
only problem is that sometimes they can be hard
to set up. This Qurtner Racing
carburettor is
bigger than standard but fits onto the standard
stubs and takes the standard airbox. You also use
the
existing throttle and choke cables and all the
settings are already tuned to your bike's engine so
you don't have to
mess about with jets. It makes a
huge difference to the engine's pick up
Your tyres are the only part of your scooter in
contact with the road, so it makes sense to get
the
best you can. The B Whiz takes big fat tyres
and we wanted a chunky tread pattern, so we
fitted some Continental Zippy
2 tyres, Not only do
they look the part and grip like leeches, they're
pretty cheap too, As we saw in the section on
tyres,
manufacturers arc beginning to take more
notice of the needs of scooter riders and are
basing a numbe1' of their products
on the high
performance tyres they make for the demanding
sportsbike market.