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CDI Derestriction
The Aprilia RS125 comes with a CDI restriction. It retards ignition around 6000rpm so the bike can pass EU emission tests so they can be manufactured. This makes your bike perform very poor at 6000rpm and does not let the engine pull. Derestricting this will invalidate your warranty. If you bike is in warranty the best thing to do is buy another CDI and derestrict this and use it on your bike.

Derestricting the CDI?The CDI is a black box under the passenger seat. Therefore to get to it you will need to remove the tail of the bike. The easiest way to do this is to remove the rear side fairings with the tail. See the manual for more details.
The CDI will have a serial number on it? if the serial number is in the following format 071000-XXXX-XXXXX then this derestriction will work if done correctly (may still work on others).

You will need to cut out a hole in the CDI to reach the bridge. Cut out a rectangle 30mm by 10mm and 5-10mm deep.

You will see a part of a circuit board, snap this. This is known as the bridge. (If you reach glass it means you have dug too far!)
Once you have snapped the bridge, fill your hole back in with silicone, make sure its waterproof! Now there will be no environmental dip between 5000-6000rpm.

Here is a detailed diagram...

Full Power Derestriction
The Aprilia RS125 can be restricted so its learner legal, and then derestricted to full power (claimed 33bhp). To do this you will need the following items:

o RAVE controller
o Powervalve blade
o Solenoid
o Cable

If your RS125 is restricted then it will not get a significant power increase around 8000rpm. If you know the powervalve is installed but you are still not getting this increase ensure all parts are working correctly, connected, and the solenoid is set correctly.

What does the powervalve do?
The blade of powervalve goes in the barrel of the engine. This then moves up and down to increase and decrease the exhaust outlet size to give you different performances at different rev ranges. The more revs you give the bike the more the powervalve blade is pulled by the solenoid and opens the exhaust outlet.
All a solenoid is, is an electromagnetic componet. Bbasically all you need to know is it pulls a cable which is connected to the powervalve blade to pull it out to increase the gap in the exhaust outlet.

You must check your bike for the componets listed above.
Your bike may be restricted via a blanking plate. You can see this by removing your right side fairing and looking above the exhaust. It will be a small plate and have 3 bolts along it (one either side and one in the middle). If you see a blanking plate then you will need to purchase the powervalve blade, mount, and other parts see parts diagram below... Your probably best getting a gasket for it too even though there is one on the blanking plate... you can reuse them but to ensure the bike performs well and you dont get any problems get a new one...

Once you have aquired these parts remove your blanking plate and fit the powervalve into the bike.
Note, the powervalve goes in one way!
It has a tapered end on one side, this should face downwards, and the flat side of the powervalve blade should face upwards! Ensure you do this!

If you can see the powervalve mount sticking out the exhaust then you will not need to purchase it of course and you will see something like this above the exhaust...

Remove your tank...
To the right of the battery there should be a solenoid which should have a cable connected on the end of it. The cable connects to the powervalve blade that goes into the engine that we looked at before.
It should look something like this altogether...

If you do not see the solenoid and/or cable then you will need to purchase these.
Once you have purchase these parts mount them to the right of the battery, there is a place for it to be fitted, it goes on the part of the radiator frame that goes right next to the battery.

If you see the solenoid and cable, and you see the powervalve mounted in the engine but your bike is not performing as it should... then it may be a case that the solenoid is not connected! If you look on the picture above there is a connector block on the end of the solenoid, see if this is connected, it connects to the main loom which runs along the right hand side of the bike from the front all the way to the back of the bike.
If you connect it up and it does nothing then keep reading....

Remove the passenger seat and check for the RAVE unit. (just remove the two back side fairings and tail)

If you cannot see this, then you will need to buy one of these and fit it to your bike. There will be a spare connector block coming out of the main loom were it should be connected to. Once you have fitted all these parts your bike should be derestricted!!!

All you need to do now is to set your solenoid up correctly... It has adjuster nuts on it, so the cable can be adjusted. This is because the solenoid starts acting around 3000rpm (you can see the solenoid opening when you rev the bike to this with the tank off). The more the powervalve blade sits in the exhuast the better low range power you will have, but poor top end. This works vise versa. See how to adjust your solenoid below...

WARNING: WHEN YOU DERESTRICT YOUR BIKE YOU WILL NEED TO CHANGE YOUR SPARK PLUG OTHERWISE YOU WILL BLOW A HOLE IN YOUR PISTON. Despite what the manual says, the spark plug to use when your bike is full power (powervalve installed) is a BR10EG. This is because the plug is colder. When your bike is restricted you should run a BR8EG. You can change these plugs for other versions e.g. Denso plugs, Iridium plugs for smoother running.

Exhuast Derestriction
The later bikes 2003 onwards have a CAT in the expansion chamber. In the expansion chamber not the end can. To get rid of this CAT which makes your bike perform differently, get an after market expansion chamber (best buying the end can with it) or buy an earlier expasion chamber from an RS125 or take the expansion chamber off and be prepared to cut it open, remove the CAT and weld it back together.

If you are going to buy a different expasion chamber then you will have to rejet your carb. The bikes with a CAT in them are set to run rich (more oil) because the CAT requires the bike to run like this. Therefore you will need to buy a standard main jet for your carb. If you have a 28mm carb (finally got it right I normally say 26mm) then your standard main jet size is a 120. If your carb is a 34mm your main jet is more likely to be a 158(i think) You can get these for a couple of quid. This means taking your carb off and removing the old main jet, and replacing it with a new one.
The racers tend to use the standard expasion chamber because it is thicker then aftermarket ones therefore contains the heat more, and these work better with more heat. They normally just change the end can.

Removing your CAT (if your being a big man)
You will need to take your expasion chamber off the bike (see manual if you dont know how)
You need to cut your expansion chamber open where this fella is cutting it and where the white line is indicated...

Once you have done this you will be able to remove the CAT

Thats it really, dont know too much about it because I havent done it... Just weld your expasion chamber back up with the CAT removed, give it a respay (heat resistant of course) because they tend to rust like hell even if you dont ride your bike in the wet.

The expasion chamber doesnt really have anything in it anyway if your thinking this was too simple. Literally just cut it open, remove the CAT and weld it back together.

Some exhausts also have a recirculation tube that goes to the air box. You just have to cut this off and weld it up and seal up the air box.
The snorkel in the air box can be taken out too, this will let some more air in slightly and make your bike sound a lot better. Just pull the rubber out the top, or you can cut the part that sticks out. This shouldnt affect your jetting since the bike is not jetted correctly from standard anyways. If you want to be sure stick a bigger main jet in (121 on a 28mm carb). Do a plug chop to confirm. To do a plug chop see the pinned topics... under useful RS125 information.

The older bikes had a 34mm carb on. The new ones have a 28mm carb. I think it was the 98's that had the 34mm carb on then after that unless modified it was a 28mm carb. If you want better mid range power, and a better top end without affecting your petrol consumption too much get a 34mm carb. The petrol consumption is suprisingly good, it does guzzle more but you get that back in power!

All you have to do is get hold of a Deloroto VHSB 34MM and a new inlet manifold because the original will be to small and then fit it onto your bike. The standard air filter will still fit this new carb.

Well thats basically it. Your bike is derestricted...
Mods to follow to make your bike faster and all round better performance...

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Discussion Starter · #2 ·

This is how it works, the bigger your front sprocket the bigger the top end, the small it is the fast the acceleration but the lower the top end.
The bigger on the back the quicker the acceleration the small the better the top end.

The standard set up is 16/39 (this is older gearing)
That means 39 tooth sprocket on the back and a 16 on the front.

You can change the size of sprockets coherently to match others
e.g. 16/39 will be the same as 15/36 (i dont think it is but you get the picture because both sprocket sizes have been changed)

At the moment I have a 14/39 set up but thats only because the person I ordered my sprockets from sent the inncorrect front sprocket.
Basically the bike is like a rocket off the line, gear one lasts for a second then I have to cog up. The bike pulls, its fast off the mark but your soon in gear 6 and it wont reach 90mph (this is before red line which I dont do).

I ride with my Dad sometimes who has a cbr600fs. He said when I took off at the lights (I didnt blast off as fast as I could, gave the bike something to think about but it wasnt rip raw off the line) he said the front of his bike came up as he stuck with me and any quicker the front wheel would have been off the line.
My steering feels quite light when im accelerating but the change in speed is just not enough, no top end what so ever.

I have ordered a 17 tooth front sprocket, this is one extra to the standard setup. This is because id prefer the top end but without loosing hardly any acceleration. This is because its only a little 125 and with a bigger front sprocket it means I can do speeds I normally do but at lower revs, therefore giving the bike a bit of a break over long distances, plus getting that little more top end.

However, a lot of people run a 16/40 and say acceleration is noticably better without sacrificing too much top end for the benefits of being quick off the line or even 15/40.
Its personal preference really, as I like long jorneys so I dont mind loosing a little acceleration to let my engine run at those lower revs. Other may just use thier bike in town and want pure acceleration because they dont get up to high speeds.

If your getting new chain and sprockets get the best. I know they cost a lot but it is well worth it. The last thing you want is a piece of string for the chain. It doesnt have to be O-ring but it helps.
I got my sprokets (JT) for ?35 I think, and my Gold O-ring Iris change for ?40 from ebay. Thats ?75 which is far more valuable then buying rubbish sprockets and chain then having to replace them ealier then me!
If you get a half decent chain and look after it e.g. lube it, clean it then you should be alright. Just cheaper chains will need more adjustment and wont last as long. O-ring just helps keep all the lube in the chain really, makes them last longer!

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3,362 Posts
just to add to burntimes sprocket post you can use a top speed calculator to get an estimated speed in whatver gear you wish, bear in mind the calculator does not take into account drag/windspeed/friciton or any other input that will affect the overall speed of the bike so dont take its calculations as gospel just an indication !!!

speed calculator


put the settings as so -


this will give the top speed in 6th gear

this is based on aprilias spec being the rpm stated at there stated top speed and a sprocket setup of 16/39 although all aprilias sites state a 17/40 standard setup.


here are the standard settings so you can fettle ratios to your hearts content:

Gear Ratio:
1st 10/30 (0.33)
2nd 14/29 (0.48)
3rd 17/27 (0.63)
4th 19/25 (0.76)
5th 21/24 (0.87)
6th 22/23 (0.67)
use these to input what gear you want to determine the speed of.

Primary drive: Gearbox:
63/19 (3.31)
this never changes

final drive: Chain:
39/16 (2.43).
this determines what drive sprockets you are calculating. for example if you wanted to check a 15/40 setup its just a case of dividing the large number by the small number (=2.666).

· Wheelies on peds with no gear = win
2,998 Posts
here are the standard settings so you can fettle ratios to your hearts content:

Gear Ratio:
1st 10/30 (0.33)
2nd 14/29 (0.48)
3rd 17/27 (0.63)
4th 19/25 (0.76)
5th 21/24 (0.87)
6th 22/23 (0.67)
Thats wrong Tom, 22/23 = 0.95656...

That ratio is wrong on every single site.

· Wheelies on peds with no gear = win
2,998 Posts
i havent used that for the calculations, ive used 1.0454 which is what it is
That isnt the 6th ratio either its 9.5656....

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12 Posts
Setting up your suspension.

As many of you will already know, sliding your forks up through the yokes 1.5cm will increase the angle of attack and turning speed of your bike.

I did this at the weekend, and for the time it takes (10minute job) it is well worth it. Even if you dont like it you can always put it back.
You can really feel the difference, and I personally think it makes the bike feel even more stable when entering a corner fast!

Basically all you need to do is, take off the front nose cone (10 bolts!) Then get someone to hold your bike upright an be prepared to take the weight of the front end. Loosen off both forks via the bolts on the top yoke, and the 2 bolts either side on the bottom yoke.

Then get the person holding the bike to put some weight back down on the wheel, and who ever is working on the bike slide the forks up through the yokes (twist them I found was easiest) then just measure them with a ruler so they both stick out 1.5cm. I found that if you loosen them both off first, then just set one and tighten it back up then do the other one was the best method. (rememeber to tighten your yoke bolts up properly!!! its 25nm for the yoke bolts, go over them again to ensure they are all tight)

You may need to adjust the rear shock after you have done this. Remember if your riding the roads dont tighten it right up, even if you think its good because thats what you do on the track, tracks dont have big bumps around corners. If you have it too tight your rear wheel will shudder out when you lean it over and hit an uneven surface. If its too loose the shock wont be able to react in time so when it hits two bumps it will probably still be on its way up when it hits the second bump.

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Air Filters!

If your thinking of getting an aftermarket air filter hold your horses! They look good yes, get rid of the horrible box but its more then just putting it on. If its genuinely a decent aftermarket air filter then it should let more air into your engine. Therefore you will need to alter the jetting otherwise your bike WILL seize.

Basically, to put your new air filter on, simply just remove the tank, remove the old air box and put on your aftermarket air filter. A lot say they will add quite a bit of BHP but you probably wont feel the difference, just it will give a better induction noise and maybe, maybe a slight boost. Once youve fitted it you will need to do a plug chop.

Plug Chop

Basically a plug chop involves putting the bike under load at high revs

"Chopping is where the igniton is cut at full RPM while the engine is under load (4th gear ish as top is illegal speed on the road )

Hit the kill switch and get that clutch pulled in fast! Slow down and with gloves on remove a very hot spark plug.

Black maybe wet + rich
Brown = good
Grey-white = she's about to blow!

Thsi is very subjective, on some bikes like a GP RS250 Honda you need different greyish colour to your road bike. It's something you need to experiment with and try it at different times of year ie very hot day to very cold day.

You can also get different temp plugs.

Always always check the chop at standard before making rash changes. Do not adjust more than 1 size at a time unless you know what you are doing.

So if we have black plugs (assuming oil pump is working correctly and it's not just loads of oil) we need to lean off meaning a smaller jet. Less fuel to the engine.

If it's white it's running too hot. Fuel has a cooling effect so run a bigger jet to let more in.

remeber this only tells you what is happenning at FULL throttle which is the most dangerous place anyway. Other factors to alter your bike are needle position and shape.

Get a good 2T tuning book off Amazon. A lot of it is for racing but will teach you the principles."

This was posted by rgvsean

You should find your plug is white if the air filter is any better and getting more air in as rgvsean says. Therefore you need a bigger main jet for your carb. You can pick these up for a few quid, make sure its the correct one for your carb and every bike is different, and obviously all air filters is not the same so dont ask how much bigger the main jet has to be.
The standard main jet on a 28mm carb is a 120, so id be buying a 122 and 124 to start off with and see how they go. DONT USE YOUR BIKE IF ITS NOT JETTED CORRECTLY, ONLY FOR PLUG CHOPS, RUNNING RICH IS OK BUT YOUR BIKE WILL BE RUNNING LEAN WITH A BETTER AIR FILTER.

Basically its just a matter of getting the correct jet. The main jet only controls the third 60 - 100% of your throttle therefore, you will need to adjust the needle jet for the rest of the throttle 35 - 60%, fiddle about with this, make it run richer and take your plug out and check the colour after a fair few miles and jet accordingly. Finally the throttle valve controls 0 - 35% of the throttle.

Normally if your bike is not jetted correctly you will feel the effects anyways. e.g. pull the throttle and the response wont be as good because you will get a rush of air and it will take more time for the petrol to come through.

Basically... people will tell you different things and until someone puts thier bike on a dynmo and tests the different ways I wont know...

First off the snorkel/trumpets...
Take the tank off your bike and you will see your air box, coming out of it at the top will be a piece of rubber called the snrokel/trumpet... People say take the whole thing out (people like me) other says pull it out, cut the end off that went into the air box then turn it around so that the end that was outside the air box is now inside it.
This will give a better induction noise, better midrange power, however people experience bad splutter around 5-6k, change your jetting and it should go! Loads of people also say dont rejet it but I would not advise it, and definatley do a plug chop. I will put a bigger main jet in my carb when I come to do this and jet correctly.

Also, I think the bikes made after 2005 have some sort of muffling material to make it quiet, take all that crap out, to me thats just sounds like another restriction.

Also, purchase another panel filter, e.g. CMP Racing, Pipercross. These are usually washable and oiled, this will give a better induction noise too and better running of your bike. Again, id rejet not just stick it on.
You can probably do the air box mod and get away without rejetting as the bike is not affected that much, but there is more air being taken in therefore that tells me to rejet.


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117 Posts
One modification that I recomend is to adjust the oil punp flow when using a derestricted air filter. Changing jets only afect perfomance but what makes the engine live is oil, and this ins't adjusted by jets.

-To perform this, take of the left panel of the bike, take of the cover of the oil punp, and by the tensor, pul it a bit if you use a stock air filter, or even to the max if you don't even carry an air filter. Wach the exaust end for oil residuals and control the smoke of the bike.

-Other modification is to adjust the idle screw. Adjust is so the intake valve is 1mm more opened; it may let your bike for a little while a bit over the idle but that 1mm will make fuel and oil go int he engine when you cut the throtle.

-Remember to clean the rave valve frecuently and check the piston rings and the intrusion of dust into the engine. Wach the intake reeds, they are in direct contac witht the air that flows in.

-The sound of your engine at idle is revelating, hear it catiously for knowing if your engine is dry or dirty or the ball bearings aren't good.

-Desrestrictions make the bike more sensible and more that is derestricted more the maintenace and it's periods. Avoid preparations if your bike is for daily use, even more: adecuate your bike for that use.

-Use ever a very good 2 stroke 100% sintetic racing oil. Modern oils prevent from humidity, reduce gas emisions and smoke, and have very good engine protection levels. Remember thar your bikes lubrication is by separated automatic mix: very racing oils aren't suitable for that type of mixture.

I hope that this post is useful.

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The jetting is different for full power as well, so even if your keeping the same carb youll want different pilot jet, main jet and needle... and the official aprilia derestriction kit also comes with a different sized airbox inlet trumpet...

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100 Posts
And worth mentioning... new E3 RS125s have completely different carbs and CDIs... the later RS125s have throttle position sensors etc... and the CDI is rerestricted by drilling a hole in it...
how do i derestrict the cdi in my 08 rs 125 i replaced my 28mm carb which had a throttle slide sensor with a 34mm one and have a pronounced dip between 5-6 k, my cdi is different to earlier years and has 2 wire inputs and i also have no rave ecu dispite having a powervalve.
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