How to derestrict a 50cc Scooter

How to unrestrict your Scooter

Over the next days/weeks I will explain the basics of scooter tuning, starting with simple improvements like derestrict a 50cc scooter and later going deeper into engine tuning concepts like flowing or changing the engine timings. Along with that I will also explain which parts should be installed first when starting tuning a scooter and which ones need to be replaced when getting more serious. Welcome to Part 1: How to derestrict a 50cc scooter.

How to derestrict a 50cc Scooter – On a general note

Fast vehicles are dangerous. Derestricting a scooter makes it faster and therefore more dangerous to ride. Always ride within your limits and be aware that you might need a different drivers license when a scooter exceeds a certain speed or engine capacity. Also your insurance might not cover you anymore.

Removing restrictions and riding a scooter without having a valid drivers license is illegal. There are heavy fines and you might loose your license when getting caught or involved in an accident!

Why are scooter engines restricted?

There are different reasons why scooters are having restrictions applied. It can be divided into three groups:

Environmental restrictions

This can be covered quickly as I only know about the catalyst applied to exhausts. Whilst it does not directly restrict engine speed it is still recommended to remove the catalyst when tuning a scooter. A catalyst has to operate at a high temperature to perform in its intended way. Unfortunately high temperatures should try to be avoided when increasing performance (increasing temperatures equal a loss of energy into heat).

The easiest way to remove the catalyst of your scooter is to replace the stock exhaust with an aftermarket model. Alternatively you can attach the exhaust of the same scooter model without catalyst (Minarelli and Piaggio engines have usually equivalent models with a non-cat exhaust). Beware as the stock exhausts are usually much more expensive than an aftermarket part and at the end of the day you will buy an aftermarket exhaust anyways when considering tuning as a serious hobby :)

Removing the catalyst from the exhaust is much more difficult as the exhaust needs to be cut open and after removal welded together again. Whilst this can be done it is usually not worth the effort.

Some catalyst exhausts have a hose connected to the transmission housing (Piaggio). This hose is needed to keep the catalyst clean. When the catalyst exhaust is being replaced this hose should be removed and the hole in the engine block closed.

Drivers license restrictions

Different countries have different laws. Some allow riding a scooter without a drivers license and others have multiple different licenses for various engine sizes. Besides the discussed stock restrictions below there are other restrictions possible that allow you riding a scooter with a drivers license it was originally not designed for. For example here in Germany we have a very popular license class that allows riding 50cc mopeds with the age of 15 already. However the top speed of the vehicle needs to be restricted to 25km/h to be compliant.

These restrictions are usually provided by third parties which means it is not a restriction applied by the manufacturer of the scooter but a kit bought from a company that specialises in restricting scooters to comply with local drivers license laws. The kit mostly contains of an electronically limited CDI and some other parts (removal of the pillion seat, cylinder head spacer to decrease compression, etc). These restrictions are not stock and therefore need to be installed by the vendor of the scooter. This also means that all installed and replaced parts are yours. When buying an already restricted scooter make sure to receive all the parts needed to derestrict the scooter again.

Unlike with the stock restrictions, these custom restrictions are explained in detail in your operating license. This makes it easier to find and remove the restrictions.

Removing restrictions and riding a scooter without having the appropriate drivers license is illegal. There are heavy fines and you might loose your license when get caught or involved in an accident!

Custom restriction to comply with local drivers license laws

Speed limits and legal restrictions

These are the most common restrictions applied to scooters nowadays and probably the main reason why you are reading this post. In order to comply with various speed limit laws for scooters the manufacturer needs to ensure that the scooter does not go faster than the allowed speed in the country it is sold. On the other hand the manufacturer wants to build engines that perform well in terms of acceleration. This is often contradictory to the speed limit requirement as fast accelerating scooters also reach high top speeds. In oder to stay within the limits but still have a well performing engine various restrictions are applied to the engine so the scooter can receive its road legal certification.

The following restrictions can be found on pretty much every scooter sold nowadays and can be split into two categories:

What’s meant by “added parts”? These are the good restrictions. By good I mean these can be removed easily without spending a single penny (given the right tools). Examples for these are variomatic rings, exhaust dummy pipes and carburetor opening restrictions.

Restrictions through replaced parts on the other hand can’t be simply removed. They usually require the purchase of an unrestricted part or considerable amount of modification. Examples for these parts are: electronically limited CDIs, diameter restricted inlet manifolds and increased length exhaust manifolds.

Derestricting the scooter will increase performance considerably allowing for a much faster acceleration and also a higher top speed (usually about 75km/h). Fuel consumption usually increases but in some cases can be lower or remains the same.

The most common scooter engine restrictions

Exhaust restriction

The exhaust restriction is applied to most scooters and can be easily removed. All that is needed is a little grinder (ideally Dremel, Proxxon, or other micro grinders). Most stock exhaust feature a dummy pipe on the exhaust manifold whereas restricted after market exhausts have a little diameter restriction welded into the down pipe.

The dummy pipe restriction

In order to remove the dummy pipe simply cut off the pipe with a handsaw or a micro grinder. It should be cut off as close to the manifold as possible. The resulting hole in the exhaust needs to be closed. Welding a washer onto the hole should do the job. Alternatively it is also possible to buy unrestricted exhaust manifolds (e.g. from Piaggio). These are bolt on solutions and cost only about 20-30Euros.

If you want to derestrict in disguise you can weld the dummy pipe back onto the exhaust on top of the washer :)

The exhaust diameter restriction

The diameter restriction is often found on street legal after market exhausts (Stage6 Replica, Yasuni Z, LeoVince, Tecnigas, etc.). Removing the restriction does not require any welding. Simply grind off the small welding spot that hold the restriction in place and it can be easily removed.

To avoid that the restriction piece falls into the manifold when grinding you should build a hook out of some wire and secure its position.

Other exhaust restrictions

There are some other exhaust restrictions. For example some stock exhausts use a very long exhaust manifold that decreases the gas flow and therefore resulting in reduced performance. These can only be replaced by buying a shortened exhaust manifold.

Another exhaust restriction can sometimes be found in the exhaust silencer of aftermarket exhausts (Yasuni). It can be removed when disassembling the silencer.

Variomatic ring restriction

The variomatic ring restriction prevents the engine transmission from reaching its maximum gear ratio, thus limiting the top speed of the engine. It should be removed as the ring causes the engine to run at a high engine revenue speed most of the time (imagine you cycle on a bike always on the first three gears even though the bike has seven). The ring also grinds into the aluminium of the variomatic over time causing it to break.

Removing the variomatic ring is difficult as the variomatic is sitting on the crankshaft which spins when trying to unscrew the nut. The safest way to block the crankshaft is to buy the special blocking tool. It costs only a few bucks and will save you a lot of trouble.

Once the variomatic nut is removed simply take out the ring that is sitting in between the two pulleys. It usually is about 5mm thick.

When reassembling the variomatic the crankshaft nut should be secured using Loctite (medium) or a similar threadlocking adhesive. If possible a torque wrench should be used when tightening the nut at 40-50nm depending on your scooter model.

Even though it’s tempting, the use of piston stoppers should be avoided. They can break the piston, cylinder head and even damage the crank shaft when too much force is applied. Have a look on eBay for the proper blocking tools available for your scooter.

Carburator restriction

The carburator is responsible for supplying a mix of petrol and air to the cylinder. It is one of the most technical parts of an engine. When the air/petrol mix supply is restricted the engine cannot perform at its full power. Throttle opening and air supply restrictions are often found on scooter carburators in order to restrict performance.

Throttle opening restriction

The throttle opening restriction prevents the rider to open the carburator completely. A limiter within the carburator blocks the movement of the slider. Simply remove the limiter and you will be able to fully open the  slider.

Petrol is poisonous and causes cancer. Ensure wearing gloves and don’t breath in the petrol gases when working on the carburator.

Carburator air supply restriction

The air supply restriction is very simple to find. Simply remove the air filter hose from your carburator and look out for plates that prevent the air flowing through your carburator when its throttle is opened.

Intake manifold restriction

The intake manifold needs to be replaced when using a bigger carburator. However, sometimes the manifold is even to small for the stock carburator. A stock carburator usually has a diameter of 12mm. This means that the manifold at its smallest point needs to have a diameter of at least 12mm as well. Otherwise the carburator can not work at its maximum performance.

Cheap replacement manifolds can be found on eBay for around 15€. They are a good investment and can be used for carburators up to 21mm diameter in size.

Air filter restrictions

It is a bit of an open story if air filter restrictions are really applied. Mostly the complex air routing of air filter increases filtering performance therefore allowing the engine to perform well under any conditions (be it a heavy monsun in India or a sandstorm in the desert). Some people say these routing channels limit air flow and therefore act as a restriction. I suggest to not modify the air filter or cut out parts. The only parts acceptable to remove from an air filter are diameter restricting nozzles as pictured below. These can be assumed safe to remove without affecting the life time of an engine.

Be careful when modifying the air filter box. More fresh air in the mix increases the temperature during the ignition process. The carburator needs to be adjusted according to the amount of air it is processing. If not done correctly the engine might overheat and can be heavily damaged.

Electronically limited CDI’s

The electronically limited CDI is one of the few restrictions that does not affect the overall engine performance over time. The CDI (Capacitor Discharge Ignition) is a black piece of electronics that handles the ignition process of the scooter. When reaching a certain engine revenue the limited CDI simply stops the engine from revving any higher by stopping ignition of the spark plug any faster. Buying an unrestricted CDI overcomes this limitation.

Please note: It is not possible to derestrict the CDI by yourself. Please do not cut any wires or try opening the CDI. All that happens will be, that you simply break it. Just purchase an unrestricted one for 50Euros and everything will be ok!

An unrestricted CDI


Can derestricting my scooter break the engine?

In most cases derestricting the scooter not only improves the performance of the engine it also allows it to perform better, longer. This is due to some restricting parts not allowing the engine to perform as it is was designed to. E.g. the variomatic ring grinds into the aluminium of the variomatic over time causing it to break, or the exhaust restrictions increasing the overall of the engine temperature by blocking the gas flow.

On the other hand when derestricting the engine it should always be ensured to setup the carburetor accordingly. Especially the main jet might need to be increased to comply with the higher engine revenues and the increased amount of fresh air supply. Your local scooter shop (if it’s a good one) should know what adjustments need to be done after derestricting the engine.

Do I loose my warranty when derestricting my scooter?

This depends on the vendor and manufacturer of your scooter. Piaggio for example gives full warranty when derestricting the scooter through a certified vendor/repair shop. For other brands this might not be the case. Best get in touch with your manufacturer or your local scooter shop and ask them if derestricting your engine has an affect on your warranty.

Which Scooters have which Restriction applied?

This is just a general note and depends on your scooter model. Also, this is only valid for the 50cc models. There are some bigger engine scooters with restrictions but it is very untypical for them to be restricted.

Piaggio 2-Stroke

Piaggio engines usually have the dummy pipe and the variator ring applied. The airbox is relatively small and can be tuned but it is not necessary if you keep your engine stock and just want to derestrict it!

Piaggio Injection

The Piaggio Injection models utilize a restricted CDI.

Minarelli / Yamaha 2-Stroke

The Yamaha Minarelli engines have a dummy pipe and a variator ring applied, similar to the Piaggio 2 Strokes.

China Engines (GY, etc.)

Almost all China engines have the limited CDI installed. Some also come with a variator ring and the carburator air intake restriction!

Honda Engines

Honda engines are often carburator restricted. Either by air intake or by not allowing the full opening of the throttle. You can also find variator rings in some engines!

How about you?

What do you think about derestricting the engine? Have you done it? Got any tricks? Let us know in the comments or the forum and I will answer for sure!


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