Derestricting a 50cc Rieju RS Sport

Posted March 11th, 2013 in News Leave a comment

We all know that the speed of a moped is limited to meet the law in certain countries. In the UK mopeds used to be restricted to 30mph, a slow enough speed when riding amongst faster flowing traffic, that speed has now been sneakily dropped to 28mph. in many other countries there is no restriction at all and in places like Holland the limit is 27mph, Sweden (where 15 year olds are allowed on the road) the top speed is a scarily slow 15mph but traffic isn’t quite so busy over there! There are various ways manufacturers use to restrict a scooter, it can range from a simple electrical restriction, which in some cases (Cagiva Mito for example) means you simply remove a fuse to release the full power, to a more elaborate type of restriction like on the Rieju RS 50 Sport.

The Rieju uses a Yamaha/Minarelli two stroke engine and Yamaha are quite particular about making sure their 50cc machines stick rigidly to the enforced limits. That means it won’t go faster than 28mph whether you’re on the flat or going down a steep hill. It also means they can be sluggish when pulling off. We took the Rieju RS 50 Sport to the Two Wheel Centre in Mansfield Woodhouse to have its full power unleashed. Although not as quick as simply removing a fuse it will still only take a dealer an hour or so to derestrict the Rieju. Two Wheel charge around £50.

Three stages

Derestriction on this scooter is a a three stage process which involves removing a washer from the variator, cutting a pipe on the exhaust muffler and fitting a larger main jet.

Pic 1

Stage one: Variator

The first job is to remove the crankcase side (you’ll ideally need a variator holding tool and air ratchet to do this job). Then remove the variator (that’s the front pulley on the photo). It’s worth noting that the variator didn’t have the usual variator tool locating holes on this engine and the alloy variator half is quite thin so it’s not a good idea to try and hold the fins with grips to remove it, or they may snap.

Pic 2 This engine has a spacer fitted to the variator, which stops the engine from using all the available gearing, therefore reducing the top speed. This is the offending washer, which needs removing. This is also an ideal time to replace rollers/belt if your engine has done a bit of mileage. Our scooter was brand new though. Once removed the variator can be rebuilt and the crankcase put back together.

Pic 3

Stage two: Exhaust

Exhausts are one of the most commonly restricted parts of a scooter. Depending on the model you’ll get washers welded into the pipe to restrict flow, pipes crimped and sometimes extra bits welded on to reduce power.

Pic 4 On the Rieju you need to remove the muffler itself and cut down the protruding bit of pipe (The small diameter centre pipe is the offending article).

Pic 5 Hold the muffler in a vice (use soft jaws or protect it with a rag) and hacksaw or Dremel it down so that it only protrudes by 8.5mm.

Pic 6 It doesn’t look like much of a cut but it makes a difference to the end result

You can now put the muffler back on. If you’re doing this at home it’s worth having a spare exhaust gasket, the original one is quite brittle and broke up as we removed the muffler.

Pic 7

Stage three: Jetting

The final stage is a bit more time consuming because you need to remove the lower plastics. This is to gain access to the carburettor.

Pic 8 Once you’ve removed the necessary plastics you need to remove the air filter box and undo the bottom of the carb to get to the main jet.

pic 9 The standard jet simply screws out (using a flat screwdriver).

Pic 10 Replace the jet with a larger 70 main jet; these are available from your local bike shop for about £3. Once fitted rebuild the scooter and check everything is as it should be.


After derestriction the Rieju is instantly transformed into a free revving machine, capable of a good 45mph. It pulls away much better, gives you more confidence in traffic, stops you hugging the gutter for safety and is also much more enjoyable to ride. Remember this isn’t engine tuning; this is simply giving your scooter the natural power it was designed to have. It’s only our draconian learner laws that force the manufacturer to stifle its power to suit our market.


If you’re sixteen years old riding a derestricted moped is illegal, if you get caught riding one you’ll get points and a fine. If you’re unlucky enough to be involved in an accident whilst riding illegally then your insurance will be void, not good. You’ll not get paid out and could face points or even a ban.

If you’re 17 years old or over and your derestricted moped (now classed as a motorcycle) meets the laws (lighting etc.) and you inform your insurance company then it is perfectly legal to derestrict your scooter. You could keep the same scooter once you reach 17, derestrict it and your slow moped becomes a much more useful 45-50mph machine without the need to replace it for a larger capacity model.

Written by 2Commute (Ian Grainger), © 2021 all rights reserved.
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