Derestricting a ZXR250

[R6_kid:Me]

just wondering how i'd know if it was restricted, and secondly how i would remove the restriction if it is restricted.... :spudwhat:

[riffer]

just wondering how i'd know if it was restricted, and secondly how i would remove the restriction if it is restricted.... :spudwhat:

How to know if its restricted FOR SURE.

Find out the stated HP of the bike. Then dyno yours. If its way lower than the stated HP, it could be restricted , or it could be tired.

Don't know about your bike, but there's a number of ways to restrict a bike.

1. Restrict the airflow (rubber bungs in the airbox, or a restrictive air filter, or baffles in the airbox)

2. Restrict the petrol to the engine. ie. small jets in the carbs

3. Restrict the air/petrol mix to the engine (restrictions in the carb rubbers (the bits between the carbs and the inlet manifold)

4. Restrict the exhaust flow (restrictive muffler)

5. Retard the ignition using a special CDI box which supplies a lesser amount of advance than the unrestricted model.

or all of the above.

In my FZR750R to derestrict takes removals of the bungs in the airbox, upping the main and pilot jets in the carbs, changing the CDI to one with a different timing curve, and debaffling the exhaust.

However, this can liberate around 30 extra HP from the motor!!!

Obviously you wouldn't get that much additional from a 250.

Why do you think your bike's restricted?

[R6_kid:Me]

i was talking 2 affman and he said that his 400 wasnt restricted like most imports, just gave me the idea that mine would be restricted, and seeing that im doing lots of work on it now then i thought i would have a look to see if it is...

[Two Smoker]

It will be restricted in speed if it is a Jap import, ie the top speed is restricted to 180kmh.....

[k14]

Yeah, I highly doubt it is restricted from power from anything apart from the exhaust. You might be able to get another 2 or 3 hp from an aftermarket one, but that is all.

[R6_kid:Me]

when you say restricted do you mean by legislation? It already has a huge after market pipe on it. So you reckon it wont top 180kph? i thought they were capable of 200kmph+

[k14]

They normally have a electronic cut out when you hit 180kph but they are also geared so that you can only do 185 or 190ish anyway. Not any point in doing it unless you are going racing, then it is easy to do, just disconnect the speedo.

[MikeL]

it is easy to do, just disconnect the speedo.

But check first to see exactly how the 180 limiting is done. On my Honda 400 it is done electronically by a switch inside the speedo which is connected to the CDI. It's possible to rewire the circuit which would be better than disconnecting the speedo cable. I haven't done it because 180 on a naked 400 with one of the less efficient braking systems produced is quite fast enough for me...

[k14]

Yeah true, i know for a fact that on my cbr there is just a little piece of metal the speedo needle touches when you get up to 180 and that cuts it out. You can pull the speedo apart and fix it that way if you wish aswell.