This site uses cookies to provide you with a great user experience and to show you relevant ads. If you’re OK with that, just continue. To find out more, please review our privacy policy.
Why are exhausts restricted?
In order for an exhaust to be road legal it has to undergo strict EEC testing to demonstrate that it conforms with quality, noise, power and safety guidelines.
If the exhaust passes the testing process it is said to be 'homologated' and issued with an E-mark certificate and the manufacturer can stamp the exhaust with the E-mark number.
In the UK an exhaust without an E-mark cannot be sold for use on the road.
As you can imagine E-marking an exhaust is quite an expensive process so normally an exhaust which comes E-marked and restricted is more likely to be a premium quality exhaust from an established manufacturer.
Most sports exhausts make far too much power to pass the E-mark testing process and consequently need to be fitted with restrictors. With the restrictors fitted an E-marked exhaust will still make more power than a standard exhaust but there will often be a further 100% increase in power if the restrictors are removed.
If you remove the restrictors the E-mark on the exhaust is of course no longer valid and the exhaust is no longer certificated or legal for road use.
The Yasuni Z, Yasuni R and Yasuni C16 City scooter exhausts have all undergone the E-mark testing process and consequently are issued with conformity certificates.
The top end Yasuni exhausts (e.g. Yasuni C20, C30 etc.) are only designed for the very highly tuned top end of scooter racing/ tuning and would never normally be used on a road moped or scooter and are consequently not available in a restricted or E-marked form, they are simply too highly tuned to be used on a road scooter.
It's worth noting that the Yasuni C16 is available in both C16 City (E-marked) and C16 Carrera (not E-marked) versions. Besides one Yasuni exhaust being E-marked and the other not they are also shaped slightly differently (the City C16 can be used with a centre stand, the Carrera C16 can't).
Despite this the 2 versions of the exhaust are absolutely identical performance wise throughout the entire rev range if the restrictors are removed from the C16 City.
Ok, so how to derestrict...
The Yasuni Z, R and C16 City have 2 restrictors fitted.
The first is in the exhaust downpipe throat and is held in place by two tack welds as shown in the photo below...
These two tack welds need to be ground out. If you don't own a dremel, now is a good excuse to buy one! It has a thousand uses and you will wonder how you ever did without one :)
'Dremel' is actually a brand name and a quality product which should last you for years, but there are also plenty of Dremel-copy products available as a kit with grinding and cutting bits for less than £20 which should be ok if you're on a budget or not going to be using it too often.
In the picture below we're using a carbide burr to grind out the tack welds but you can just use the grinding stones which come with a Dremel kit. The carbide burr eats metal away much more quicky than a grinding stone and will not wear out so quickly but is more expensive.
It's worth noting that if you were grinding a softer metal (e.g. aluminium cylinder porting work) the carbide burr will cut through the aluminium like carving butter whereas the grinding stone would be almost useless.
Ok, so grind away the two exhaust tacks being careful not to go into the wall of the exhaust.
You can now gently break away the restrictor with a screwdriver and it will drop down a little into the exhaust.
Using the Dremel again clean up any metal from the tack welds remaining on the exhaust wall to make it smooth and tip the restrictor out of the exhaust.
This is the first restrictor removed!
The second restrictor is in the rear silencer.
Undo the two nuts which hold the silencer can together and pull it apart.
Here you can visibly see the Yasuni quality which you won't see in any other scooter exhausts. All joints are perfectly matched and sealed with O-rings. On many other exhausts the silencer clamps together against the cylindrical sleeve. This means on many exhausts the sleeve is actually part of the structural srength of the silencer and causes the ends of the sleeve to chip away and the silencer sleeve can start to rotate and consequently leak resulting in the silence quickly falling apart.
The Yasuni silencers have an internal structure which means the cylindrical sleeve is not part of the structure as should always be the case!!
Yasuni uses genuine stainless wool and fibreglass for it's silencer packing, which again is typical of Yasuni quality, nearly all other scooter exhausts use a budget wadding wool which is fine but needs to be replaced more regularly to prevent the exhaust becoming noisy.
Use gloves handling the fibreglass, it will be very itchy (like loft insulation) if you get it on your skin.
In the picture below you can see the restrictor in place in the silencer core.
There are two tack welds holding this restrictor in place, one you can see in the photo the other is on the other side.
Time to get the Dremel out again, or you can just use an angle grinder for these if you have one.
Grind or cut away the tack welds and remove the rear restrictor.
Reassembly is of course simply the reverse process. Don't forget to grind off the E-markings from your exhaust as it is no longer road legal :)
