Restricting a 450cc to 250cc?

[Nick11]

Hello,

I'm new here, so bear with me. When I found this site, I thought the resources available were informative and the question I would like to ask would be best answered here.
I recently passed my A2 test (U21) which allows me to ride any bike up to 33bhp. Yet, I'm looking to buy an Enduro bike for green-laning. However, I have thought of question and excuse my ignorance.

Is it possible to buy, say a CRF450X and restrict it (on the contrary to derestricting) to match the same output as a 250cc? 48.5bhp to 33bhp?

In many ways, when I successfully pass the two year restriction (before you can ride any bike), I can destrict the bike and gain a 450cc power without having to buy another bike - a combination of both and is cost effective.

Any ideas?

Thanks

[Chr!S]

Yes they are called 33bhp restricter kits


F.I International is the company who sells them in the UK.

[Kickstart]

Hi

Possible to restrict power like that. Even possible to reduce the engine capacity, although the cost would be silly.

Basically with a slide carb the restriction would likely be to just stop the throttle opening fully.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Nick11]

Fantastic!. Thanks for the responses.

I took a look at the site and the available restrictor kits, but it seems that they do not offer a CRF450X kit, although offer a WR450F kit. Just dropped them an e-mail and see what happens.

BTW, can't you go to a dealer or a reliable local garage service for the restriction? I mean, the process is quite simple with no complications.

[Kickstart]

Hi

The law just says the bike must be under the relevant power limit and power to weight ratio limit.

You could just go to a local place to get them to restrict it, if you can find one happy to do so.

Most larger bike use CV carbs, and on those opening the throttle does not directly affect the fuel mixture. So washers after the carbs just restrict the airflow like the throttle does, and the CV bit of the carb sorts the mixture out. With slide carbs the throttle does directly affect the mixture which is why using washers after the carbs is likely to result in it running VERY rich.

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[G]

Note that a 250cc will not specificially output 33hp.
For instance some 2 strokes may be over 55hp, or more when tuned.

While other 250cc bikes can make as little as 12hp or so.

As mentioned above, it's 33hp that's the important number.

I know it's now what you're asking, but you might want to consider if the CRF450X is a good bike for your purposes (which I don't know).

[Nick11]

I am aware of the specifications and requirements. In that respect, I can see why most get confuse with 4 strokes and 2 strokes when it comes to recognising the engine capacity.

Ideally, the CRF450X is a great all-rounder for rural backwaters and its 250 sibling isn't much point as I would end up selling the bike when the restriction terminates in 24 months - would be a wasted £3500.
I'll have a hunt around and see what can be done. Some time needs to be spend on this issue to ensure that a green light is given.

Thanks to the above for providing a good foundation to my question.

[G]

Not sure what you mean about confusion between 2 and 4 strokes and engine capacity. Note that 4 stroke 250s can also make over 33hp for sports biased engines.

Have you checked you're happy with the service intervals on the CRF450X?
I don't know the specs of that model, but I would guess even though it's detuned, they might not be great for an 'all rounder'.

By the way, more stuff you didn't ask - but most would consider it fairly wasted money to spend that much on a bike to restrict for two years, however if you've got the money which you're happy to spend, might as well.