They may be a bit big for a 1300 crossflow, I used 35mm bore ones from a gpz1100 on a 1600 engine and they were about right , I am now using 38mm gsxrs on an 1800 zetec and suspect they may be a bit to large for good response at low throttle openings but have only just started mapping them .
I have seen Bmw bike ones on ebay go very cheaply and think they are about 34mm but would need injector bosses fitting to the manifold as they dont have them fitted to them.
Paul

I also used the GPZ1100 T/Bs on my mildly tweaked 1600 X/F, easy to respace , comes with T/P/S (although I'm having problems with it) . Made the manifold and airbox myself easily and best of all they were cheap. Would recommend getting the injectors cleaned and tested though, From what I've learnt 35/36mm seems to be in the ball park for size. Too big or too large can cause problems.

P.S Did you manage to sell yours Paul?

[Edited on 13/5/07 by rusty nuts]

The absolute maximum that a xflow port can be safely ground to is 33mm diameter (throughout the port not just at the manifold end). This would be a full-race 1700 head costing lots of money, as it requires a lot of metal removal. I suspect your 1300 is to a lower spec so avoid the temptation to go too large- a 32mm throttle body would be more than adequate, and would work well if you upgraded to a ported 1600 engine.

It's a standard 1300, albeit rebuilt and with a 0.030" rebore. I'm planning on putting in a BCF2 cam and fancy going the injection/megasquirt route.

From the replies it appears 32mm throttle bodies would be suitable, but which bikes would have been fitted with them? Would it be smaller GPZ's or are there others?

The other option would be bike carbs/megajolt. Would this be a better way to go?

I want to keep the 1300 for the forseeable future, because I like the way it drives. I just want to see what I can get out of it while keeping it usable on the road.

I also want to keep any installation under the bonnet, and get rid of the "tractor" air filter.

David