Converting A 250 SUPERDREAM TO A 400

[cbradley400/4]

Does anyone know how easy (or difficult) this is please?

I have the chance to buy a 250 with a 400 engine and carbs but am wondering whether I need anything else such as the loom and other electrics?

[Athame57]

I remember the CB400n had a halogen headlight that the 250 didn't have, and also twin discs up front too, so plumbing and the front end might be more work than electrics.
Oh, the clocks were different too. 

[Bryanj]

I know the generators were different but not sure about the cdi boxes, check part numbers

[McCabe-Thiele (Ted)]

There are two UK Superdream sites, this has been covered or you can ask.

They have downloadable parts books and manuals like here.

[McCabe-Thiele (Ted)]

Different number of connections for the CDI box.
Different drive sprockets.

[BigAl (Alan)]

The main wire harness part No. 32100-443-000 fits both models. There is also a rear lighting sub-loom, part No. 32200-443-000 that  also fits both models.

[cbradley400/4]

Thank you to all repliers : that is all most helpful

[McCabe-Thiele (Ted)]

My Superdream is the 400NA model, lots of later changes to the front suspension & twin brake calipers. Also some of the later Reverse Comstar wheels don't fit earlier models iirc.

[cbradley400/4]

Another point has occurred to me and I wonder if anyone can answer this please?

The V5 has the 250 frame number as the vin but still the 250 engine number.

I know the frame number cannot be changed and must remain with the registration number but how easy is it to change the engine number if the engine is changed to a 400?

My understanding is the bike has not yet been registered as a historic vehicle so assuming you can change the engine to the 400, the additional road tax would have to be paid to put the bike on the road and of course it would also need to be MOT'd and insured.

[cbradley400/4]

My Superdream is the 400NA model, lots of later changes to the front suspension & twin brake calipers. Also some of the later Reverse Comstar wheels don't fit earlier models iirc.

Yes thanks, I seem to recall those changes back in the day when the bikes were current.

[Bryanj]

Yes you can change the engine number on the V5 BUT  changing to 400 MAY be considered a change big enough to stop you getting historic tax category