Carb and jetting
- PHBH28BD: main jet 115 restricted, 120 unrestricted.
- The 123’s 34 mm carb has no jet stack in the manual.
- A 34 mm carb on a 122 is a mod, not this table.
RS125 · 1993–2006
Carb and jetting
Stock jetting is the PHBH28BD in Haynes. A 34 mm carb on a Type 122 is a modification, written up with the parts it needs. The two records are not the same carburettor.
| Stock | Popular upgrade | |
|---|---|---|
| Carburettor | Dell'Orto PHBH28BD, Haynes, both power columns. | A 34 mm body on a Type 122 that left with the 28 mm carb. The one named most often is a Dell'Orto VHSB 34 LD. |
| Also on record | The research brief pairs a VHSB 34 with the Rotax 123. Hartrusion says a few early 122s had that 34 mm carb as stock. Read the stamp. | PJME and Hartrusion both say the 28 mm inlet manifold will not take the 34 mm Dell'Orto. Jetting has to be done on that bike. |
| What this table is not | A jet stack for a 34 mm body. Do not put the PHBH jets into one. A seller that calls a VHSB 34 LD the OEM carb for both engines does not match Haynes. | |
The manual's unrestricted column is labelled 20 kW. Open-bike homologation figures already on this site run about 21–23 kW and change with the generation. Those figures stay ontuning. They are not edited down to 20 kW.
| Item | 11 kW restricted | 20 kW unrestricted |
|---|---|---|
| Carburettor | Dell'Orto PHBH28BD | Dell'Orto PHBH28BD |
| Starter jet | 70 | 70 |
| Main jet | 115 | 120 |
| Pilot jet | 62 | 62 |
| Slide needle | BN 264 | BN 266 |
| Float needle valve | 250 | 250 |
| Pilot screw | Not published | Not published |
| Idle speed | 1,150–1,350 rpm | 1,150–1,350 rpm |
Pilot-screw turns are Not published in the photographed pages. Idle is the chapter 1 range, 1,150–1,350 rpm, for both columns.
Plug, cables, free play
- Spark plug: NGK BR10EG. Electrode gap 0.5–0.7 mm. Plug torque 20 Nm.
- A derestriction blog on this site names a BR8EG as the plug you are leaving. The manual extract does not. Both stay listed; the manual's plug is the BR10EG.
- Throttle cable free play at the twistgrip: 2–3 mm. Choke cable free play: 2–3 mm.
- Fuel: unleaded, minimum 95 RON. Tank 13.0 litres. Reserve 3.5 litres.
Float height and needle-clip position are Not published. The "250" above is the float needle valve size, not a height.
Notes from readers
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Sources
Research brief dated 24 October 2026. Where this page says “the brief”, that is the sourced master plan behind the first edition.