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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.

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