Safety message: Modification of the CDI involves cutting into sealed electrical components. Ensure the ignition is off and the battery is disconnected before starting. Use high-quality silicone to reseal the unit afterward; moisture ingress will cause the CDI to short-circuit, potentially leaving you stranded or causing engine damage.
The "CDI Drilling" (or "Bridge Cutting") is a legendary rite of passage for Aprilia RS 125 owners. This modification removes the intentional "power hole" that Aprilia programmed into the ignition curve between 5,000 and 6,000 RPM to help the bike pass drive-by noise and emission tests.
This applies specifically to the Nippondenso CDI (typically marked with serials starting with 071000-) found on Rotax 122 engines from the late 90s through the Euro 3 models.
1. Locate the CDI
The CDI is the small black box located under the pillion seat/tail unit. You will need to remove the tail fairings to access it comfortably.
2. Identifying the "Bridge"
On the back of the CDI (the side filled with a rubbery potting compound), there is a specific spot where a circuit board "bridge" sits just beneath the surface.
On Euro 3 models (2006+): There is often a faint dimple or a 10mm x 30mm rectangular outline marked in the plastic/potting.
On Older Models: You generally measure roughly 3-5mm up from the bottom edge, centered horizontally.
3. The "Drilling" or Cutting
You don't actually need a drill; a sharp Stanley knife or a small flathead screwdriver is often safer to avoid going too deep.
Carefully pick away the rubber potting compound in a small 1cm x 2cm area.
You will reveal a small, protruding piece of green circuit board with a copper trace (the bridge).
Break the bridge: Use a small pair of snips or a screwdriver to snap/cut that trace. This tells the ECU to stop retarding the ignition in the mid-range.
4. Sealing the Wound
Once the bridge is cut, the bike will pull cleanly through 6,000 RPM. However, the internals are now exposed.
The "Secondary" Restrictions
Drilling the CDI is only 1/3 of the battle. If you don't do the following, the bike will still feel "restricted":
The Power Valve (RAVE): Ensure the blanking plate has been replaced with an actual blade, solenoid, and cable.
The Intake: On Euro 3 bikes, the airbox has a "snorkel" that is often restricted. Owners usually remove this or replace it with the "open" version.
Jetting: Cutting the CDI changes the combustion timing. You must up-jet the carburetor (typically moving from a 132 main jet to something in the 160-185 range depending on your exhaust) to prevent the engine from running lean and seizing.
Critical Carburetor Adjustments
You cannot simply unlock the electronics without adding more fuel. Running a de-restricted CDI with "learner-legal" jetting will result in a seized engine.
Main Jet: Typically moves from a 120/132 to a 155–165 (for 28mm carbs) or 158–160 (for 34mm carbs).
Needle Position: Dropping the clip (raising the needle) by one notch is often required to richen the midrange.
