Identify your RS125
- Read the plate, then the casting.
- A 1998 registration can be a Rotax 123 or a 122.
- Haynes lists a PHBH28BD for both power columns.
VIN and engine
Read the plate, then the casting.
A 1998 registration can be a Rotax 123 or a Rotax 122. The number plate will not tell you which. This decoder uses only the positions the research brief defines, and it marks every other year letter To verify.
The reading will appear here. Nothing is sent anywhere.
Where the number is
From the MP model on, the plate is on the frame to the right of the headstock. Early GS, LA and MP00 bikes have the number stamped on the frame, sometimes with a sticker and no plate.
- Positions 1–3
- ZD4 means Aprilia from the MP model on. GS and LA numbers start GS or LA instead.
- Positions 4–5
- Model code: GS, LA, MP, SF or PY.
- Position 6
- Variant. The brief’s examples are 0 for open and A or B for restricted. MPB uses B for the bee-tail generation, so it is not a complete key.
- Position 10
- Model year, from the MP model on. The sourced letters are in the table below.
Year letters the brief lists
| Code | Model year |
|---|---|
| 1 | 2001 |
| 2 | 2002 |
| S | 1995 |
| T | 1996 |
| V | 1997 |
| W | 1998 |
| X | 1999 |
| Y | 2000 |
This table is the brief’s list for the years this site covers, 1993 to 2006. A code that is not in it is marked To verify until it has been checked on a known RS125 plate from those years.
Position 9 is not defined in the brief. North American VINs use it as a check digit. That has not been confirmed for these Italian plates, so the decoder does not check it.To verify
Rotax 122 or Rotax 123
| Rotax 123 | Rotax 122 | |
|---|---|---|
| Casting | Left rear, by the engine number | On top of the left crankcase, by the cylinder |
| Carburettor | Dell'Orto VHSB 34 | Dell'Orto PHBH 28 |
| Haynes 4298 carb table | Lists a Dell'Orto PHBH28BD for both the 11 kW column and the 20 kW column. It does not give a jet stack for a 34 mm carburettor. Both records stay. Read the stamp, then thecarb specs. | |
| Ignition | SEM | Nippondenso CDI |
| Where you find it | Extrema / GS, and much of Europe and the UK until about 1997–98 | Italy from 1995, then the later bikes through the 2006 RSV-style |
A 34 mm carburettor on a Type 122 that left with a 28 mm carb is a common upgrade, not proof the engine is a 123. Hartrusion also says a few early 122s had a VHSB 34 as standard. Read the casting and the stamp. The stock-versus-upgrade record is onmods: carburettor.
Italy moved to the Rotax 122 in 1995, and a 1998 bike can be either engine. That mapping is the research brief. Haynes 4298 does not add a year-by-year engine list, so the casting is stillTo verify. Piston codes, ring gaps, clutch plates and gear ratios differ. They are on the engine specs page, kept as Type 122 and Type 123.
Sources
- Haynes manual 4298 (Aprilia RS50 and RS125 1993-2006) (opens in a new tab) — Haynes
- Differences between Rotax 122 and 123 (opens in a new tab) — Hartrusion
- Modellübersicht RS 125 2T (opens in a new tab) — Hartrusion
- Storia e modelli (opens in a new tab) — rs125.it
- RS 125 replica decal sets by year (opens in a new tab) — Decalmoto
- Aprilia model list (opens in a new tab) — Motorcyclespecs
- RS 125 review and buying guide (opens in a new tab) — MCN
Research brief dated 24 October 2026. Where this page says “the brief”, that is the sourced master plan behind the first edition.