One idea at a time in focus mode
The licence boundary, and the hardware the existing sources name, without a pinout.
Before you start
Your own risk. Wrong jetting or timing can seize the engine. This is information, not advice.
How many steps: 3
Step 1 of 3
An A1 licence stops at 11 kW. Read that first.
Licence, MOT, insurance or a seizure.
GOV.UK: category A1 is a motorcycle up to 125 cc, 11 kW and 0.1 kW/kg, from age 17. After a CBT only: L-plates, no passenger, no motorway. An open two-stroke is not that motorcycle. You still need the bike registered, taxed, roadworthy, MOT’d when the rules say so, and insured at least third party. The sentence an insurer wants after a derestriction is To verify with that insurer.
Step 2 of 3
Open bikes are about 21 to 23 kW, by generation.
The research brief’s open figures, already on the tuning page: Extrema / GS 23 kW, round-light about 22 kW, bee-tail MPB0 22 kW and SF 21–21.5 kW, RSV-style PY0 21 kW. Restricted columns in that brief include 11 kW, and a 5 kW MPA1. UK bikes are often described at 15 bhp. That is a third sentence. It is not the same as 11 kW, and it is not the same as the open figure. Haynes labels its unrestricted carb column 20 kW. That label stays the manual’s label. It does not rewrite the homologation figures down. Hartrusion’s matching point is the one on the carb page: a 34 mm carb was not a 25 kW engine. The GS with that carb is the 23 kW bike.
Step 3 of 3
The restriction is a plate, ignition, catalyst and jets.
Licence, MOT, insurance or a seizure.
The derestriction notes, from the research brief and the blog they cite, name four pieces: a powervalve blanking plate instead of the RAVE blade, a Nippondenso ignition retard around 5,000 to 6,000 rpm that varies by unit, a catalyst in the expansion chamber from 2003, and a jet and plug change when the pipe changes. Haynes, for the PHBH28BD only: main 115 on the 11 kW column and 120 on the 20 kW column, pilot 62 in both. The plug in the manual is an NGK BR10EG. Do not put those jets in a 34 mm body. The old jets with a catalyst removed are how these engines seize. Which codes left the factory with a plate, and the pinout of any ignition unit, are To verify. This site does not publish a pinout, a wire colour or a solder bridge.
This guide is done. Your place stays on this device.
GOV.UK: category A1 is a motorcycle up to 125 cc, 11 kW and 0.1 kW/kg, from age 17. After a CBT only: L-plates, no passenger, no motorway. An open two-stroke is not that motorcycle.
You still need the bike registered, taxed, roadworthy, MOT’d when the rules say so, and insured at least third party. The sentence an insurer wants after a derestriction is To verify with that insurer.
Legal and safety. Changing the restriction does not change the licence you hold. Riding an opened bike on an A1 or a provisional entitlement is a licensing offence, not a tuning detail.
Source: GOV.UK licence categories, and GOV.UK legal obligations
The research brief’s open figures, already on the tuning page: Extrema / GS 23 kW, round-light about 22 kW, bee-tail MPB0 22 kW and SF 21–21.5 kW, RSV-style PY0 21 kW. Restricted columns in that brief include 11 kW, and a 5 kW MPA1. UK bikes are often described at 15 bhp. That is a third sentence. It is not the same as 11 kW, and it is not the same as the open figure.
Haynes labels its unrestricted carb column 20 kW. That label stays the manual’s label. It does not rewrite the homologation figures down.
Hartrusion’s matching point is the one on the carb page: a 34 mm carb was not a 25 kW engine. The GS with that carb is the 23 kW bike.
Source: Research brief on the tuning page, Haynes 4298, and GOV.UK
The derestriction notes, from the research brief and the blog they cite, name four pieces: a powervalve blanking plate instead of the RAVE blade, a Nippondenso ignition retard around 5,000 to 6,000 rpm that varies by unit, a catalyst in the expansion chamber from 2003, and a jet and plug change when the pipe changes.
Haynes, for the PHBH28BD only: main 115 on the 11 kW column and 120 on the 20 kW column, pilot 62 in both. The plug in the manual is an NGK BR10EG. Do not put those jets in a 34 mm body. The old jets with a catalyst removed are how these engines seize.
Which codes left the factory with a plate, and the pinout of any ignition unit, are To verify. This site does not publish a pinout, a wire colour or a solder bridge.
Legal and safety. This is a description of hardware the sources name. It is not permission to ride the result, and it is not a set of instructions for opening a particular bike.
Source: Derestriction guide, Haynes manual 4298, and the RS 125 blog
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