Put a 50bhp Rotax 257 engine in an Aprilia RS125 Frame

Tips for stock (standard) RS125

	Use a good quality 100% Synthetic Oil, preferably Silkolene Comp 2+, Motul 600, Castrol TTS or Shell Advance VSX RacingX or M
	Change the original spark plug for a better one, for instance an NGK B10EG or B10EG-V
	Use 98 octane fuel
	Every 4000KM, de-carbonise the cylinder and clean the exhaust valve to ensure smooth running
	Use a good quality synthetic gearbox oil like Motul, Castrol or Mobil
	Oil the with Chain WAX every 250KM
	Clean the bike and perform regular maintenance on it (like oiling cables, etc..)

Further modifications

	Drop the forks down through the yokes by about 1.5CM for an increased angle of attack and a faster turn in speed
	Use a thicker (heavier) fork oil for the front forks
	Fit a set of EBC "Double-H" sintered brake pads for increased braking performance. The reference number for the front pads is : EBC FA126HH
	Fit braided brake lines
	Replace the standard exhaust for an Arrow or Giannelli exhaust system (Arrow performance graph at the bottom of the page)

RS125 Restrictions

Let's clear the subject of restriction's up to avoid any confusion! There are 2 (TWO) types of restrictions that the RS125 can have :

The first restriction is a power restriction, it will limit the RS125's maximum power to 15bhp (or 11kW). The restriction consists of the lack of a Powervalve (instead a blanking plate is fitted so there's a fixed exhaust port height), Powervalve electric motor (opens the powervalve), Powervalve control unit, some sort of exhaust restriction (the pipe diameter is restricted with some sort of insert into the exhaust) and the matching carburation changes to reflect the restriction. This restriction is only found on some RS's (the 15bhp or 11Kw versions) to make it legal for 16 year olds to ride it in some countries. If your bike can only do about 120-130KM/H and there isn't a sudden power increase at about 8-9,000rpm then it's probably restricted. Another way to check for the lack of a Powervalve is to put the bike into neutral and keep it idling, then rev it slowly to about 3,500rpm. At about 2,500rpm you should hear a clicking sound from the engine. This sound is the powervalve closing and opening. If you don't hear any of this, then your bike hasn't got a powervalve. Take a look at the powervalve picture at the bottom of the page,

The second restriction causes the power dip between 5,000-6,000rpm and it does this by retarding the ignition (spark) in this rev range. This is done so that the RS125 (being a 2-stroke) can be homologated and pass the new European Union  emissions and sound tests. This can be removed by modifying the CDI. I've done this myself and it makes the bike much easier to ride around town as you don't have to slip the clutch or go down a gear to get into the powerband. The old RS125 ('98 and before - Rotax 123 engine) didn't have this restriction. Read below on how to de-restrict the RS125 CDI.

How to de-restrict the RS125 CDI to remove the environment dip :

This modification ONLY works on the CDI's with the following CDI serial number format :

 071000-XXXX-XXXXX

Take a look at the following schematic :

With a sharp knife, dig out a rectangular hole in the BACK of the CDI (where the silicone is) about 30mm by 10mm in size and about 5-10mm deep. It may take some time to dig the hole out completely because the silicone that's used in the CDI is very strong. Once you've dug out the hole, you'll notice a bit of circuit board, this is commonly known as "the bridge". Using a screwdriver or a pair of pliers, break the bridge. After you've done this, fill the hole you've dug with Silicone, make sure you do it properly so that it's waterproof and no water gets in!. After you've done this, there should be no more environment dip between 5-6,000rpm!!

For an easier to follow guide on how to de-restrict the CDI, take a look at the following image that I scanned in of a sheet of paper that was forwarded to me by the organizers of the Aprilia Challenge.

WARNING : This modification invalidates the warranty and if you screw up your CDI don't come blaming me!! 

Standard Dell'Orto PHBH 28mm carburettor settings

PHBH Carburettor diagram at the bottom of the page

Arrow performance graph (included with Arrow exhaust)

Bear in mind that the jetting suggestions are relevant to the 34mm carburettor and not the 28mm found on modern RS125s.

RS125 Engine/Gearbox/Bike Schematics

Download  (863KB - ZIP File)

(click on photos to enlarge, back button on browser to go back)

RS125 CDI photo
CDI and powervalce control unit
Restricted Aprilia RS125 vs Full-power RS125 dyno graph
Aprilia RS125 Powervalve (RAVE)
Dell'Orto PHBH 28mm carburettor diagram

Standard Aprilia RS125 Ignition map (with environment restriction between 5-6,000rpm)