Scooter tuning

So you want more power from your scooter. Welcome to the club.

Scooter tuning is very popular throughout the world. A vast array of aftermarket performance parts are available for many applications, from circuit or drag racing to high performance street duties.

Should you start upgrading parts on your scooter? If the scooter is still under warranty, and you want more power then be very careful as performance modifications usually void the warranty. You have been warned!

Also many countries have laws in regards to the top speed or maximum KW output of mopeds (Generally 50cc scooters). Make sure you check this or you could find you’re breaking the law in your country.

If you can’t control your need for power or don’t have a warranty on your scoot – then read on.

Before starting, have a read of our maintenance article and make sure that your scooter is in good working order. No point tuning a scooter that won’t be up for the challenge: If you deem your machine ready then the work can begin!

Derestriction

(Mostly applies to 50cc scooters)

Many modern 50cc scooters are restricted. This is usually done to limit the top speed.

This is done by:

1. Restricting the exhaust pipe.
   
2. A washer/ or similar limiting the movement of the variator.
3. CDI (computer distributed ignition) which limits the maximum rpm of the scooter.

Once you’ve worked out what is restricting the scooter and replaced/or removed that restriction. You should find the bikes full potentional. Be wary of spending hours de-restricting your scooter if you’re planning on further upgrades that will result in restricted parts being binned. It may pay to combine the de-restricting with power upgrades. i.e. instead of spending ages drilling out a restriction in the standard exhaust pipe, replace the entire system with an after market model; the end result will equal more power.

Exhaust

This should be one of your first choices when tuning a scooter. This is especially true for a 2-stroke motor. The shape and internal diameter of the exhaust has a large impact on the power of a two-stroke motor. In a four stroke the increase won’t be as pronounced, but still is key part of the tuning process.

Intake

There are three parts to the intake of most scooters:

Air filter and box

Manufacturers create scooters that are quiet. They do this at the expense of some power. The engine has to work a little harder to suck the air through a small intake hole, into an air-box, which reduces intake noise and through a foam/paper filter that also removes dirt from the air.

If more power is to be made then more air and more fuel will be required. More fuel means bigger jets in the carburettor; jet size selection depends on level of modification done to the engine.

Carburettor

An engine can only ever flow a certain volume of air through the carburettor (carb) and intake manifold. This will quickly become the limiting factor for most 50cc scooters. Upgrading the carb usually means purchasing a larger unit. This will increase performance due to the creation of a larger opening at wide open throttle, therefore more air can be taken into the engine. Ultimately performance may also be limited by the manifold so it is a good idea to mate a larger carburettor to a larger manifold.

Manifold

The manifold takes the air and fuel mixture from the carb and delivers it to the engine via reed (or less often rotary) valves. The manifold has an internal diameter which limits the amount of air/fuel that the engine can take. Therefore there is little point fitting a 28mm carb to a manifold with an internal diameter of 16mm. The carb will be able to flow more fuel than the manifold will accept. The manifold usually features reed valves. Reed valves are like a one-way switch, air and fuel can flow into the engine, but not back into the manifold, this means the mixed fuel and air flows into the chamber.

Chamber

The cubic capacity of an engine is the largest contributing factor to ultimate horsepower in naturally aspirated engines. The reason for this is the amount of power generated is greatly affected by the volume of combustible material i.e. fuel and air the engine can burn each cycle. Getting 10hp from a 125cc engine is a lot easier than from a 50cc, therefore, increasing capacity is an easy way to vastly improve the power of your scooter. Removing the existing piston and head and replacing it with a larger capacity combination is an easy and effective power-up.

Other Upgrades

There are a variety of other methods of acheiving greater horsepower from your engine. Some of these include; turbocharging, nitrous gas and supercharging... this discounts of course the validity of tying a few clydesdales to the scooter...

We will delve further into these more extreme options in another installment...

Driveline

The majority of modern scooters use a Continuous Variable Transmission (CVT) system, this is often referred to as an 'automatic' or 'twist and go" transmission. There is a front and rear variator joined by a belt. As the bike accelerates the front variator pushes the belt to the outside or top, creating a bigger “gear” . At the same time, the rear variator lets the belt move to the centre, allowing a smaller “gear”.

When tuning begins the maxium power output of the engine moves to different points in the Rpm range, therefore it is important to alter when the variators allow the belt to move. If too early then the engine bogs down, like changing into fifth gear in a car while only travelling at 20kph. Another possible scenario is that the engine revs too high, this will again slow the scooter down and increase wear and tear on the engine by running it at the red line for increased periods.

One of the ways the driveline can be altered is by changing the weight of the rollers in the front variator, this will change how and when force is applied to the belt. A lighter set of rollers will move the belt out lower in the rev range. The converse will happen with heavier rollers.

There are many after-market ‘high-speed’ variators, These work in two ways firstly they increase the surface area for the belt, in other words increasing the size of the top gear, allowing more top end speed. In addition to this the ramp that the rollers use is on a steeper angle, giving sharper acceleration.