The Laws of Scooter Tuning

In this article were going to be discussing a question we get asked quite often, which is: “I want my scooter to go faster, where do I start?”

There are a few levels of scooter tuning which completely depend on what you want to do with your scooter. The first thing to do is to decide what you’d like to be able to do with your scooter, whether it be take it out to the race track or just keep up with the flow of traffic with a little extra power to spare. Scooter tuning is a huge industry particularly in Europe with many race series touring around, and large events like the Malossi Trofei – with hundreds of bikes and riders drawing huge crowds as a legitimate race series. However you don’t need to turn your scooter into a race machine to keep up with the traffic a little better.

Most scooter riders who want to boost the power of their scooter are happy to do so in stages, as to get the most bang for buck. So we’ll start with the most basic level, and work our way up to the extreme track bike. The great thing with scooter tuning is that you can just stop where you feel you’re happy with the scooters performance, as long as parts are done in the correct order. Below is the order which we feel adds both the best performance increase, and makes the most sense to add and modify parts in.

Stage 1

For many scooter riders or scooter tuning enthusiasts, stage 1 is all they’re looking for, just to give their ride a little extra power. This stage is the addition of a performance exhaust, which also needs to be accompanied by a few small changes in the carburettor jetting and often transmission and clutch to suit the heightened power curve of the motor. This just means that with the addition of a performance exhaust, your motor will produce more power, but will have to rev slightly higher to produce it. This means that the factory transmission and clutch settings need to be adjusted to get the maximum benefit. The basic concept behind a performance 2 stroke exhaust (often called an extraction exhaust) it the effect of its expansion shaped chamber. Instead of just providing back pressure (resistance against the flow of gasses leaving the motor) performance 2 stroke exhausts ‘suck’ the burnt gasses from the motor allowing it to far more efficiently produce power.

There are different levels of performance 2 stroke exhausts, from basic to full race. The exhausts we sell are designed for use with a standard 50cc cylinder as well as an upgraded 70cc cylinder. Different exhausts are available for different scooters, however for most makes and models the Arrow Street and Extreme exhausts are quite appropriate

For scooter owners who aren’t savvy with a rattle gun, a performance exhaust can still be installed with great benefit without changing the rollers or clutch springs – however the jet change is essential. This change is normally approximately a 20% – 25%  increase depending on your specific scooter, and if you are removing any air restrictors whilst installing the exhaust (many standard 50cc’s have air restrictors either in the airbox or carburettor). Some 50cc’s (TGB scooters in particular) may also require a replacement CDI to remove the rev limiter. Some CDI’s can be modified to remove this limiter.

If it sounds daunting, any good motorcycle mechanic will find it an easy task to fit and tune. We also have an instructional video below which should give you a good idea of how to install and tune a performance exhaust.

Stage 2

The 2nd stage of scooter tuning is the installation of a 70cc cylinder kit. The installation of a 70cc kit is normally the biggest improvement in terms of power increase made by any single upgrade. 70cc cylinder kits are specifically designed for each scooter to replace the standard 50cc cylinder and piston. The increase is due to a couple reasons, the additional 20cc’s of capacity is the most obvious contributor – however 70cc cylinders have a higher performance port mapping designed to make more power than the ports on the standard cylinder (ports being the windows on the side of the cylinder which are responsible for allowing fresh air and fuel to enter the combustion chamber and expelling the exhaust gas).

This upgrade is a little bit more in depth than installing an exhaust, and requires some prior mechanical experience to carry out. If you’re pretty handy, you shouldn’t have a problem working it out – and the kits we sell come with instructions as to the process involved with installing the kit. Fortunately 2 stroke motors are fairly simple machines, even without a lot of mechanical experience there are a plethora of instructional videos on YouTube which may give you some more confidence going into the installation as to what to expect, and how to carry out the installation.

The crucial part is installing the piston correctly without bending, distorting or losing the circlips. Once installed the tuning process is essentially the same as tuning for a performance exhaust, increase the jet by 20% – 30% and if needed adjust the transmission and clutch to suit.

The installation of a 70cc kit will usually almost double the power of a scooter when installed with a performance exhaust, as well as drastically increasing torque. The practical benefit of this on most scooters is being able to pull away from a stand still faster than most cars, being able to maintain higher speeds of between 80kph – 100kph depending on your particular scooter and how well it has been tuned.

At this level in particular the difference becomes substantial between Air Cooled motors and Liquid Cooled motors.

It is important to note that with your scooter at this stage making approximately twice the power it has been factory designed to produce, moving parts will tend to wear faster and have a higher tendency to break if not maintained correctly. Having a scooter tuned to this level will require more servicing and a higher cost to maintain in most cases! But when looked after properly and serviced on time with quality parts its fairly unlikely that you’ll have an inconvenient malfunction occur.

Below Left is a video of a Liquid Cooled 70cc kit being unboxed,  so you can see what these its come with and what they replace from your standard engine. Below Right is an unboxing of an Air Cooled 70cc kit.

  

Stage 3

The 3rd stage of scooter tuning is about bringing the performance level of your transmission up the the same level as the combustion side of the motor. This stage can be done a few difference ways and to a few different levels. The transmission of a scooter is mostly made up by the Variator, Belt, Clutch and Diff Gear (reduction gear). Below we’ll go through these 4 main elements in their order in the drive train.

The Variatior is the gearing control of the scooter, which works via centrifigal force allowing the scooter to increase of decrease its gearing ratio from its maximum values. Installing a performance variatior not only increases the maximum value
(top speed) in most cases but has increased efficiency in reaching top speed, and giving the rider access to power at all times. A well set performance variator usually allows the scooter to rev more through its acceleration, without over revving – and being that more revs generally means more power, a performance variator is better able to deliver the power from your motor to the road.

A performance variator usually has the effect of smoothening the acceleration out, giving a consistent and predictable ride, which can give the rider more confidence throughout the speed range of the scooter. A performance variator is also built tougher, designed to take
more punishment than most standard variators. On top of this performance variators are usually more sensitive to small changes in roller weight tuning also.

The Drive Belt is the bridge between the variatior and the rear wheel in many respects. The CVT gearing system encompasses two parts, the Variator (at the front, driven by the crank) and the Torque Driver (at the rear, connected to the clutch and then the rear wheel). The torque driver is tensioned by the torque spring (also called the “contra spring”) which acts as a tensioner for the belt against the variatior by placing demand on the belt. This balances with the weight of the rollers in the variator and the revolution of the motor and forces the transmission back into a lower gear when the revs of the scooter decrease. The belt not only carries the weight of both the scooter and the rider, but also the force of the motor – and as you might imagine this is not only a crucial role but a hard wearing job. Add to this that with stage 1 & 2 completed the motor is now producing twice the power, putting twice the strain on the belt. It isn’t hard to see the benefit of installing a performance belt. A performance belt is designed and made to be stronger, to be able to handle higher load and cope with more punishment. Performance belts often bare the addition of composite materials like Kevlar and Carbon. The draw back of these materials is that they make the belt much stiffer, which can have an effect on the operation of variator (not necessarily negative, but not always desired). Because of this Malossi make two ranges of performance drive belts, the ‘Kevlar Belt’ and the ‘Special Belt’. The Special Belt is stronger than the original belt, while still remaining similarly flexible to the original belt as not to effect variation too much, where the Kevlar belt offers the maximum strength and durability but is however more stiff than the special belt.

The Clutch is responsible for delivering power from the torque driver to the diff gear.

Its job is to release the scooters weight and load to the engine smoothly, allowing the motor to rev during the initial moments of accelerating without dumping the entire load of the scooters weight on the motor at once, softening it with gradual load transfer. The operation of the clutch is often explained in the opposite to this, referring to it as delivering engine power to the wheel. Both of these explanations are true. Scooter clutches are centrifugal in a similar way to the variator, however function much more simply. Essentially they’re three shoes, mounted via pivots and held together by springs. As the clutch spins with the rotation of the torque driver these shoes are centrifugally forced outward on their pivots as the centrifugal force overcomes the resistance of the springs, stretching to allow the shoes to expand and grab onto the clutch bell (which encases the shoes of the clutch). Stiffening these clutch springs means more RPM is required to cause the clutch shoes to pivot and grab onto the clutch bell – allowing power for the motor to start transferring to the rear wheel. A performance clutch is generally also tougher, and has higher grip material on the shoes (similar material to a brake pad) allowing them to grip more suddenly and result in more rapid initial acceleration. There are a few different types of performance clutches available, with higher end racing clutches coming which a whole host of finer adjustments for the really meticulous scooter tuner to adjust away to their hearts content. many inexperienced scooter tuners choose a more simple options, such as the Malossi Fly Clutch – which is adjusted only by changing the 3 springs to vary what RPM the clutch engages. Heavier springs require more centrifugal force to stretch, and therefore allow the engine to rev more before engaging.

The Diff Gear is the reduction gear between the clutch shaft in the transmission and the drive shaft which the rear wheel is bolted to.

Often called the ‘final drive’ this is the last stage of the transmission system, acting as the medium between the rotation of the clutch bell and the rear wheel. The job of the Diff Gear is to reduce the rate of rotation from the clutch bell to the rear wheel according to the size of the wheel and power of the engine. Without a reduction, scooters would be awfully sluggish off the start, like trying to accelerate from a standstill in 5th gear driving a manual car. Installing a performance Diff Gear allows you to play with the gear ratios – usually lowering the overall ratio to achieve a higher top speed. On a standard 50cc scooter, there isn’t normally enough power to warrant sacrificing some for higher top speed. However, on a scooter which has already been tuned up to stage 2 you have some power to play with. On some scooters (TGB 50cc’s and SYM Jet 50’s in particular) this upgrade can be added earlier on than stage 3 without having too detrimental of an effect on the acceleration. This exception does not apply to all scooters however. The Diff Gear kits come with ratio’s to allow you to work out the percentage of difference to the standard, normally on a well tuned scooter 10% – 15% is a good place to start.

Final note: it is important to note that the transmission of a scooter only works well when balanced finely. All elements need to work together properly. For instance, adding a Diff Gear kit may require a slight change to the weight of the rollers to counteract the difference slightly. The pursuit of fast scootering is often won or lost in the transmission!

  

Stage 4

The 4th stage of scooter tuning is upgrading the carburettor and inlet system. Stage 3 and 4 can be done in either order without much consequence. We recommend upgrading the transmission first, to bring it up to spec with the motor before adding more power at the inlet – however this is just our preference.

Installing a larger carburettor allows more air and fuel into the motor, producing more power. Depending on your mechanical and tuning ability this can be the more complicated and fiddly side of tuning. Most 50cc scooters come standard with between a 12mm and 17.5mm carburettor. For performance purposes these can be replaced with a 19mm or 21mm carburettor. The sizing refers to the size of the inlet on the carb, a larger inlet means more air.

Malossi make a series of Carburettor kits in both 19mm and 21mm for the specific purpose of improving the intake on 50cc scooters. These kits are scooter model specific in most cases, with all the appropriate parts included to fit the upgraded carb to the your specific scooter. The kit includes the carb, manual choke kit, mounting plates for the choke kit and in most cases 2x airbox stuffers (small cylinders with a flat edge on one side). To install the stuffers, drill 2 appropriately sized holes (matching the diameter of the stuffers) in the inlet side of the airbox. The stuffers have a small lip at the end of them, the idea being that they just slide in and snap into place giving you tidy looking holes for additional air flow. Standard airboxes typically restrict air flow, many also have rubber boots at the airbox air inlet which can be removed to help reduce this restriction as well.

It is EXTREMELY IMPORTANT that you only install the stuffers on the inlet side (air that has not yet been filtered). Generally speaking, most airboxes draw air through the outer side of the airbox, through the filter in the centre, with the filtered air passing into the carburettor via the inner (wheel side) of the airbox. The stuffers in this case would need to be installed on the outer side of the airbox. The additional air that is allowed into the airbox must pass through the air filter.

It is also recommended to change the reed valve with the carburettor, to allow more air flow. The reed valve acts as a one way valve on the inlet of the engine, keeping compression inside by not allowing air out of the inlet between strokes. Performance reed valves usually have larger petals, made from Carbon Fibre rather than metal like original petals. The higher flexibility of the carbon fibre allows for greater responsiveness, with the larger inlet size on the petals complimenting the increased air intake of the larger carburettor.

Stage 5

The 5th stage of scooter tuning is changing the internals of the motor, to allow for higher compression. Specifically this is changing the crankshaft, crank bearings and seals to high speed, high compression performance parts. This is a stage really only recommended for liquid cooled scooters. Whilst more power can be achieved by doing this to an air cooled scooter, it isn’t an efficient increase in power factoring in the cost involved.

The second benefit to doing this is that many higher end performance 70cc kits require high compression cranks, or longer stroke cranks. for the few scooter enthusiasts who dare to venture into this territory it can open up a whole new world of full race level performance. This is not for the light hearted. A race bike on the road is an absolute pig to ride, often described as ‘On or off’ – meaning they like to be ridden full throttle all the time. A cylinder at a race level must also be matched with a race exhaust, which are obnoxiously loud – They’re made for the track.

This step is the difference between a street and a race machine. Likewise to take this step further with race level cylinder kits and cranks – other parts such as the transmission and carb should also be upgraded to get the full performance from the race level motor.

Higher end cylinder kits such as the Malossi MHR Team cylinder range require special cranks to run properly. Changing the crank out for a high compression crank will increase the performance of your motor, however as it is required to completely remove and disassemble the casing of the motor to do this – the added benefit of not hugely significant compared to the cost and effort involved with doing this.

The real benefit is being able to upgrade the cylinder kit to a bridge ported cylinder kit, which will produce far more power. This upgrade usually needs to be accompanied by a higher performance ‘race level’ exhaust to truely extract the full performance from the higher level cylinder and crank. A ‘Bridge port’ is the type of exhaust port used in high end cylinders, its the largest exhaust port possible on the inside of a cylinder. The faster you can expell exhaust gas in a 2 stroke, the more power you can make.

The Malossi RC-One motor takes this to the next level. The RC-One is a replacement crank casing, which allows the Malossi Testa Rossa 94cc kit to be installed. This is one available on scooters fitted with Piaggio Hiper2 motors (without significant engine mount modification).

This is a big job! Definitely not something that the average rider would want to take on without a decent level of mechanical experience prior. This is about as far a scooter tuning goes.

After this, there are further scooter tuning upgrades such as inner rotor ignitions, crank case porting, oversize transmissions, pod filters, bigger carburettors and even turbo kits – however stage 5 is as far as we go.

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If you want to see what parts fits with your scooter see what is available  at the scooter street

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**ALL Scooter Tuning performance modifications listed here are for race use only. We accept no responsibility for incorrect or illegal use of parts that we sell** (Translation: Have fun, but be sensible)