performance
tuning:
tuning to change a scooter's output
info on 2-strokes
info on 4-strokes
This does not necessarily mean giving your scooter higher
top speed. Remember in New Zealand your 50cc scooter is
only legally allowed to be capable of 50km/h. However
you can change it so that it still does 50km/h up hills,
or with a trunk full of bricks, or into a headwind. Modifying
your scooter to increase the torque output is certainly
beneficial as it will help you maintain speed, and get
off the line at traffic lights a little quicker. Torque
is what accelerates your weight against anything trying
to resist it, including gravity and inertia. Modification
may mean that your scooter runs more efficiently or accelerates
better to get you clear of traffic.
about scooter engines - overview
The majority of 50cc scooters and many bigger scooters
have 2-stroke (also "2-cycle") engines. These
have higher output than 4-stroke / 4-cycle engines (as
found in most cars) however they are difficult to keep
running as efficiently. When it is a 50cc scooter, overall
efficiency is still much higher if you consider that an
engine around 40 times smaller than a car's is moving
one person around. The parts are made of materials similar
to other motorcycle/car engines, and a typical Japanese
2-stroke 50cc will rev to 6.000rpm under normal use. The
main parts and systems are similar, they need air cleaners,
a device for mixing air and fuel, the combustion engine
itself, and an exhaust and muffling system.
2-strokes:
Two stroke engines generally produce more power than four
stroke engines because they provide twice as many power
strokes at a given rpm. They are less efficient so the
output figure is usually not exactly twice that of a four
stroke.
Two stroke engines are simpler in design, not having moving
valves, cams or oil sump systems.
Sports/racing tuning of a two stroke engine is based around
the ports and exhaust. So if you want to get more performance,
look at your exhaust first. A performance exhaust for
a 2-stroke engine is called an expansion chamber. This
allows exhaust to expand in the optimum volume as it cools
and exits towards atmospheric pressure. Well-designed
chambers supposedly use sonic waves reflecting from the
reducing conical areas to aid scavenging and help to stop
intake charges escaping through the open exhaust port.
A two stroke chamber's shape is something like a long
cone with different, calculated steps where the cone gets
bigger to form the chamber. The cones angles affect the
powerband width and amplitude. These cones form primary
and secondary chambers and are unique for each engine,
depending on port shapes and exit velocities. Timing of
scavenging of the exhaust pulses is important to create
power. Although even factory exhausts (except the very
worst ones) should have some form of taper, the sports
expansion chambers for 2-strokes are designed better.
4-strokes:
Four stroke petrol engines are used in most bigger motorcycles,
and in nearly all cars. Recently, in order to comply with
domestic and international emissions laws, four stroke
scooters have been produced. These traditionally produce
less power than a two stroke engine but run a little more
quietly and efficiently.
Unlike a 2-stroke, 4-stroke engines need an oil retaining
lubrication system, valves in the head and cams to drive
these valves.
Sports/racing tuning of a 4-stroke engine involves enabling
free breathing of the engine and increasing the compression
ratio (forced induction or by raising the static compression).
This is where multivalve heads and turbos or superchargers
come in. However as the saying goes, 'there's no replacement
for displacement' i.e. increasing the size of the engine
is the way to get more power easily. Scootling can supply
82-94cc engine kits for the 4 stroke Hondas including
'Smart' Dio AF61 engine, Today and Metropolitan.
Some sport variants of Japanese and Italian 50cc scooters
already have 4 valve heads and Electronic fuel injection.
tuning to factory settings:
returning your scooter to the
factory OEM recommended settings
This could be called a "tune-up". Your scooter
was designed to run with certain restrictions in the intake
and exhaust, so carbon or unburnt oil deposits in exhausts
and clogged air cleaners can reduce the efficiency and
power of your scooter.
Drivetrain:
There is not a lot to adjust on CVT style transmissions
(i.e. most scooters), usually it is wear on parts that
need to be replaced that occurs. However the final drive
gear oil can become sludgy and the increased viscosity
drags. Occasionally replacing your gear oil with high
grade oil improves performance.
Carburettor:
Deposits and varnishes from fuel additives can accumulate
in the bowls and jets. This can cause rough running, poor
starting and lack of power in scooters. If your scooter
runs roughly, will not rev, or is difficult to start,
the carburettor may need cleaning. Some fuel system flushes
work to an extent and can be used to prevent build up
of some deposits.
Engine:
Scooter engines with very high mileage can lose power
through piston blowby. For 2 stroke scooter engines this
means cylinder pressure can leak on compression strokes
and primary pressure from the crankcase can be lost on
the piston downstroke. Both will contribute to lost power.
Other deposits in the engine especially in exhaust and
induction passages and reed valves can be a detriment
to your scooter's engine efficiency and performance. Completely
blocked mufflers are sometimes found on scooters that
are run cold too often without opening the throttle enough.
This means the fuel oil is not kept hot enough to remain
vaporised. Instead of exiting the muffler it sticks to
the internal surfaces. Once a scooter muffler is blocked
replacement is the best solution. Check out our parts
page for what may be available for your scooter.
If your scooter is going slower now than when you bought
it, or slower than others of the same model (and you are
not heavier) it is probably a combination of worn drive
parts and need of a tune up. Scootling imports these
drive parts so if your scooter needs to regain some life
please contact us.
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