Carb Size Definition

[motorhead13]

Hi,
I've got a 250 that I've turned into a bobber that I'm putting a 400 engine in. I got the carbs with the engine and I've read that its vital to have the right carbs for the bigger engine (obvious I know). I want to check that they're the right size, so how would I tell the difference between the carbs from my 250 and the carbs I got with the 400? I take it measuring a certain area would tell me this?

Thanks

 

[xschris]

The sohc xs400 uses a mikuni bs34 carb and the xs250 used a bs32 carbs. You measure the I.D. of the carb that goes into the manifold.

 

[motorhead13]

Thanks for that.
And I assume it should be 34mm for the 400, 32mm for the 250?

 

[xschris]

Yes.

 

[motorhead13]

Thanks.
That's a pain for me as it seems the carb I got with the 400 engine only measures 32mm (I take it that's the ID for the side that connects to the engine?) so must be for a 250.
I assume I could use that carb just to test the engine and get it running then get the right size carb for using the bike?