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Bee-tail

  • New tail and a right-hand duct. Rotax 122 and a PHBH 28.
  • A catalyst arrives in the expansion chamber in 2003.
  • Chesterfield is a scheme again from 1999 to 2005.
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Generation 3 · 1999–2005

Bee-tail

The 1999–2005 bee-tail RS 125: Rotax 122, PHBH 28, MPB then SF, and the first catalyst in 2003.

Updated 24 October 2026 · Two-stroke

Rounder fairing and a lower tail. A diagram, not a photograph.
Years
1999–2005
Factory code
MPB (1999–2002), SF (2003–2005)
Engine
Rotax 122
Fuel system
Dell'Orto PHBH 28
Ignition
Nippondenso CDI, with the environmental dip called out on these bikes
Bodywork
Wider, rounder fairing, a lower bee-tail subframe, five-spoke wheels, and one air duct on the right.
Power
MPB0 22 kW open. MPB1 11 kW. SF open 21–21.5 kW.
Restricted and open
MPB1 is the 11 kW code. From 2003 the SF has a catalyst in the expansion chamber, and from 2004 a secondary air system. Both choke a full-power build if they are left in place.

Key changes

  • New body: wider and rounder, with the lower tail that gives the generation its name, five-spoke wheels and a single air duct on the right.
  • MPB covers 1999–2002. SF covers 2003–2005. Both are Rotax 122 bikes with a PHBH 28.
  • 2003 adds a catalyst in the expansion chamber. 2004 adds a secondary air system.
  • The Tuono 125 naked of 2003–04 is the sibling, not an RS 125 generation.

Common problems

  • The catalyst from 2003 chokes the exhaust.
  • CDI ‘environmental’ dip around 5–6,000 rpm.
  • Sticking powervalve or a seized solenoid.
  • Speedo drives wear out.
  • Crank bearings, and exhaust corrosion.

Special editions and replicas

Per Hartrusion, as recorded in the research brief, “Replica” means the decal scheme. The mechanical bike is the standard model of that year and code.

Liveries filed on this generation
LiveryYearsStatus
Chesterfield1994 Extrema, and 1999–2005 bee-tailVerified. Not listed as a 1998 scheme.
Tetsuya Harada1998–2000Verified
Valentino Rossi1998 and 1999Verified
Diablo Black2001Listed in the generation record. No separate line in the verification table.
GP-One / GP1 and SBK2003Verified
Manuel Poggiali2004–2005Verified
Marco MelandriBee-tail eraYear to verify

The full list, including schemes that are not verified, is on the generations hub.

The bee-tail is the Rotax 122 generation that most people picture when they say “a late two-stroke”: a rounder fairing, a tail that drops, five-spoke wheels, and a single intake duct on the right. The engine question is quieter than it was in 1998. These are 122s, with a Dell’Orto PHBH 28. The new questions are the catalyst, the powervalve and the crank.

MPB, then SF

MPB is 1999–2002. MPB0 is the open bike at 22 kW in the brief. MPB1 is 11 kW. SF is 2003–2005, and the open figure drops slightly, to 21–21.5 kW. The SF is also the bike that gains a catalyst in the expansion chamber in 2003 and a secondary air system in 2004. The RSV-style bike that follows keeps a catalyst and calls the air system SLS under Euro 2. If you are buying a 2003–2005 bike for the way a 1999 one rides, you are not buying the same exhaust.

The frame number on these is a ZD4 plate. MP with variant B is the MPB reading used on this site’s decoder. SF is positions 4–5. The year letter sits in position 10. The brief’s table includes X for 1999, Y for 2000, 1 for 2001 and 2 for 2002. It does not list 2003, 2004 or 2005. Those ISO codes are 3, 4 and 5, and they are To verify against a known plate.

What goes wrong

The catalyst chokes the pipe. The Nippondenso CDI has a flat spot the brief calls an environmental dip at about 5–6,000 rpm. The powervalve sticks, or the solenoid seizes. Speedo drives wear. Crank bearings fail. Expansion chambers rot. None of those is a torque setting. They are the inspection list for guide 1 and the reason a cheap SF can cost more than a tidy MPB once the pipe and the crank are honest.

MCN’s intervals still apply to the top end: rings around every 5,500 miles, piston and barrel around every 10,000 miles, and a warm-up to 60°C before you use it. Premium two-stroke oil is the grade advice in that same note. The pump stroke is To verify.

Liveries, and the Tuono

Rossi returns for 1999, on this body. Harada runs 1999–2000. Chesterfield is a bee-tail scheme from 1999 to 2005, which is the documented Chesterfield, as against a 1998 one. Diablo Black is 2001. GP-One / GP1 and SBK are 2003. Poggiali is 2004–05. Melandri is named for the bee-tail era and the year is To verify.

The Tuono 125 of 2003–04 is the naked bike from the same family. It is not an RS 125, and it does not belong in the replica list.

Sources

Research brief dated 24 October 2026. Where this page says “the brief”, that is the sourced master plan behind the first edition.