Too much choke can flood your Aprilia when you are starting it up.

Fixing the problem is easy

1. Remove the seat from your bank
2. Remove the bolt holding your tank in place and lift it up
3. The HT lead is easily seen on the RS125 so take it off your plug and torque out your spark plug.
4. Put your RS125 in second gear
5. Keep your RS125 turned off and the clutch lever out
6. Push your RS125 along (as if you were bump starting it)
7. The cylinder will crank over and blow any excess fuel out of the cylinder

Why not have these updates delivered directly to your inbox saving you time and ensuring you recieve content as soon as it becomes available?

Click here to subscribe to Aprilia RS125 Tuning by email.

How to fit steel braided brake lines to your Aprilia RS125

Thanks toAndyS_RS on TJ Tuning who inspired this post.

Fitting braided brake hoses will not give you greater stopping power, but it will give improved feel which is crucial to effective braking. This guide describes how to bleed the front brake. The process is the same for the rear brake, but bleeding is easier and can generally be done without removing the calliper.

Install the steel braided hose and bleed your brakes

• Empty the line by bleeding the brake.
• Connect hose to the nipple and loosen
• Pump the brake and it should eject fluid, which you can collect in your container.
• Keep the brake attached to the bike while you do this.
• Once the reservoir is empty, stick a clean rag in, soak up remains and prevent intake of dust.
• Loosen the master cylinder banjo bolt (beneath the banjo bolt there is a small ball bearing, be careful not to lose it).
• Use a rag to mop up any drips.
• Take the loose end of the hose, place it into your container and then place the container as low as possible.
• Fluid should drain into the container.
• Disconnect the hose from the caliper once it has stopped.
• Remove the calliper from the fork but there will still be fluid in it so keep it upright.
• With the hole into which brake fluid flows carefully positioned over your jam jar, squeeze the pads apart and it will eject most of the remaining fluid into the container.
• Remove the pads from the calliper and clean it thouroughly.
• Check that your new hose is of equal length to the rubber hose it will replace.
• Ensure it is properly routed.
• Take the new bolts from the box and reinstall the calliper
• Connect both ends of the hose and tighten up the new banjo bolts.
• Ensure that the small ball bearings have been replaced and that copper washers have been installed on either side of the new hose.
• Fill the reservoir half full with your new brake fluid and start bleeding the brake(this will take a while as the system needs to be primed with new fluid).
• Top up the reservoir as required.
• When you reach a point that you feel is acceptable take the bike out a few times and the leaver will get firmer with each use.
• On your return, flush a few more measures of fluid through the line and top up the reservoir (the instant you open the bleed valve it will go spongy, but close it up and it will get firm very quickly).

Diagnosing the problem when your bike won’t start can be difficult. Check out this guide for common reasons for the RS125 not starting. Work your way through the checklist from top to bottom.

RS125 Non-Starter Checklist

• If there is a nick in a tube or you have a leaky carburettor, your fuel could have escaped and evaporated over the course of a few hours (Lift your filler cap and check that there is fuel visible in your tank).
• Someone could have played with it since you last rode the bike or you might have forgotten.
• Put the bike in neutral and push along with your feet (or have someone push you).
• When you have reached a good speed, put the bike into SECOND gear and hit the starter button.
• If she starts up, pull the clutch in. The problem would appear to be in the starter motor.
• The starter relay can be found behind the radiator and the connection means that it is possible for wires to fall out of the unit.
• If you can bump start the bike and the wires are all connected, the problem could lie within the relay.
• Turn the engine over and make sure that a good volume of air is coming out of the exhaust.
• If possible, take it off the bike and look for blockages.
• Make sure the choke is not flooding the engine.
• Remove the seat and lift the tank up.
• Either remove the spark plug or take a good plug that you are certain work, and connect it to the HT cap.
• Touch the end of the plug to the frame via the insulated cap as you are in for a shock (haha) if you hold the plug itself.
• Hit the starter button and look for a spark.
• Check the original plug in the same way to make sure that it isn’t the source of the problem.
• Make sure that the HT lead sits snuggle onto the plug.
• Make sure that everything is plugged into the CDI as it should be.
• This is located underneath the pillion seat. Look for bare or cut wires.

Adjusting the carburettor needle can make a huge difference to the way your bike behaves. Begin by removing the tank (pop the seat off, remove the bolt through near the head stock and pop the tank up). Turn the fuel tap off and remove the fuel line.

Undo the screws that hold the top of the top of the carburettor in place and lift out the slide. If you are using a 34mm carburettor, you can unscrew the top and lift out the slide. Disconnect the slide from the cable by compressing the spring with your fingers and pushing the cable down into the slide. Do not let the spring fly off!

Once the cable has been disconnected, turn the slide upside down and allow the shim to drop out. This is a small plate onto which the spring pushes in order to keep the needle down. Once you’ve done this, you can remove the needle. There will be a circlip on the needle.

If the clip is on the lowest groove then you will need to upjet your carb. Otherwise, try moving the clip down to the next notch (towards the tapered end) and take your bike for a spin. This process pushes the needle up into the carburettor slide more, allowing more fuel to squeeze past the tapered end.

If moving the clip has improved performance, but it is still not perfect, try moving the clip to the bottom groove. If that still isn’t right, upjet your carburettor and reset the clip to the middle of the needle.

If these adjustments make the performance of your engine worse, try moving the clip up a notch and test the engine.

Derestrict your bike to unleash its full 33bhp!

The Aprilia RS125 restricted to 14bhp for learners or derestricted to 33bhp for those who hold a full license. This guide will tell you where to find restrictions and how to remove them.

How can you tell if your RS125 is restricted?

• Ride it and look for a significant increase in power at 800rpm
• Lift up the tank and check the right hand side of the battery compartment to see if a powervalve solenoid has been installed (the solenoid is tubular and mounts via two bolts).
• If you don’t get an increase in power but the powervalve has been installed then the system is not working correctly.
• If it has been fitted ensure that the cable is correctly connected to the blade and the system moves freely (check out this guide for loosening a seized powervalve).
• Test the solenoid by disconnecting the 2 pin multiplug that connects the solenoid to the wiring harness.
• Earth one of these pins and connect the other to the positive terminal on your battery (it will move if it is working)
• If it has seized then it will need to be replaced.

Removing the exhaust restriction

• Bikes produced since 2003 have a catalytic convertor in the exhaust expansion chamber. You can either
• Purchase a new expansion chamber and end can (you MUST rejet your carb)
• Take the expansion chamber from an older bike
• Cut open your pipe to remove it and weld it back together.

Installing a powervalve and solenoid

• Installed the blade with the flat side facing up and the tapered side facing down (when retracted, the slope on the end of the blade lines up with the exhaust wall).
• Install the solenoid on the right hand side of the battery box.
• Connect the cable to the blade
• Adjust the solenoid once it is in place.
• The more the powervalve protrudes into the exhaust port, the more low end power you will have and the less top end power you will have.
• The less it protrudes, the less low end power you have but the more top end power you will have.
• You must now install the RAVE unit.
• Remove the tail fairing to get to this area.
• The RAVE unit is a similar size to the CDI unit (also underneath the pillion seat) and you will find a multiplug in this vicinity that connects to it.
• Change your spark plug or you will destroy your piston.
• A restricted bike should run a BR8EG
• A derestricted bike should run a BR10EG.

Removing the CDI restriction

• The stock setup retards the ignition at around 6000rpm so the bike can pass emissions tests.
• This causes very poor running at this engine speed and you will notice a drop in acceleration.
• Derestricting the CDI will invalidate your warranty, so buy another from ebay if you bike is still in warranty and derestrict that.
• The CDI is located under the pillion seat. Remove the tail fairing to get to it.
• The back of the CDI is filled with rubber and the bridge is underneath it.
• Remove an area of about 10mm from the bottom of the CDI and about 15mm either side of the centre line of the unit.
• You will eventually reach a bridge between two terminals.
• Snap this and then refill the hole with silicon.

Carburettor

• Newer bikes have a 28mm carburettor whilst the original bikes had a 34mm carburettor.
• Fitting the 34mm carb gives better mid-range performance and better top end power without affecting your pertrol consumption significantly.
• Get hold of a Dellorto VHSB 34MM and a new inlet manifold (the original will be too small).
• The original airbox should be fine with the bigger carb.