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Restriction

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There has been alot of questions about restriction on the forum lately which has prompted me to write this FAQ or fact sheet on the subject. Firstly a few points about restriction on the bikes:

• None of the CBR400/CBR250 were power restricted as standard.
• All CBR400's after the RJ were speed restricted at 180km/h (approx 112mph).

speed restriction
power restriction

Speed restriction:

Speed restriction is administered by the CDI unit, on the 400's there is a sensor built into the speedometer which triggers upon the bike passing 180 km/h. As far as I know this restriction is only on the 400's.

Characteristics of speed restriction:

• bike will power seemlessly until it reaches 180km/h where it will sound rough, the CDI at this stage cuts the spark to certain cylinders, prohibiting acceleration.

Removing the speed restriction:

Alot of people ask how to remove the speed restrictor on the CBR 400, I usually ask "Are you mad?" in response. But seen as there is the demand for the information I will provide as much as I can.

The speedo contains a sensor, which appears to be like an infra-red or light sensor. On the rotating axle of the speedo there is a disc which has a notch on part of the outside of the circle, this notch passes through the sensor when the bike hits 180km/h. Part of the de-restriction process is to stop this sensor being triggered.

The next problem is that the CDI does not see the sensor information anymore. This I'm am unclear about but I have heard that a resistor can be used to fool the CDI into thinking that it is getting the apporpriate signal from the sensor in order for it to oporate properly. One of the wires is a signal wire and it is possible to short this to a 12V+ wire which will give the CDI the required signal, to enable free revving.

Power restriction

Power restriction is most commonly implemented by placing washers between the carburetors and the intake ports of the engine, these washers limit the gas flow into the engine, hence limiting the fuel getting to the cyclinders. These kits are usually researched for each model to produce the specific power output. In Ireland the learner limit is (33bhp).

Characteristics of power restriction

• Power restriction will do exactly as it says on the tin, restrict the power.

Removing the power restrictors:

Simply remove your carbs from the engine block and in the rubber tubes connecting the engine to the carbs you should find 4 washers (one in each tube), remove these and you will now have full power.