British 250

[steve234]

I have been considering building a British 250 for VMX & DT as opposed to trying to get a jap bike and was wondering what peoples thoughts or experiences were.

[jimson]

I've got a BSA frame with a XL350 engine to go in it  I'm thinking of putting rego on it when its done it should be a cool ride something different  jimson

[LWC82PE]

ok im guessing you would want to go with a late model C15 or B25 BSA? they are pretty slow but you can do a bit of work to them. ive seen big bore kits for C15 non ebay. i really think you would need a good ignition, larger carby, something more modern like a mikuni, a good larger diameter free flow exhaust and some serious porting in the head and bigger valves. theres also mods to do to the bottom end to convert the timing side main to a bearing instead of a bush in the C15. a fair few dollars would need to be spent to make it enjoyable to ride and at least feel quick and responsive because as thay are std they are a bit of a slug.

so my thoughts are if you dont want or need to be higly competitive and dont mind something thats going to be a little slower than go for it.
have you ridden stock british 4 stroke 250?

as i can see from that triumph, i bet that is no where near std inside.

[steve234]

Yeah i was thinking the later B25, Triumph TR25 and staying away from the C15. Weren't the Triumph's pretty much a BSA anyway?

As far as being competitive goes i'm not to concerned as i am happy just being a part of it.

[LWC82PE]

yes pretty much the same but pobably like the same as the B50 and its triumph badged quivalent and they are not 100% the same and there is more to it than badge engineering.

[grouty]

Steve, if you want more info on tuning the little B25 motor have a look around
www.b50.org
The site is mostly the B50 and it's derivitives, but if you do a search you will find quite a bit on the smaller B25.
Ed V in the states has made a few B25 motors that will give the 500's a run for their money. The B25 responds well to methanol (if you are allowed to use it). But as mentioned earlier, to get power out of these little motors it will cost.
CCM here in the UK tried a much modified B25 in a standard CCM frame in 1973. A rough outline of the modifications can be found in the book "Rolling Thunder". But even with all the time and money spent it would not keep up with the Jap 2 strokes at the time.

[steve234]

Cheers Grouty,

There sure are some nice machines out there. There was someone selling reprints of Rolling Thunder over here a few years ago so i'll try and look him up.

[grouty]

The new and updated book "Rolling Thunder" is published here in the UK in the next week or so. I have ordered mine via the "WH Smith" website.
http://www.whsmith.co.uk/CatalogAndSearch/ProductDetails-Rolling+Thunder+-9780981727028.html

Hopefully that link will work.
Another person to talk to is Mark Cook at performance Engineering here in the UK.