So my Spitfire does not have an intake manifold on it and I was thinking about swapping on a either individual motorcycle carbs or throttle bodies. Does anyone have any tips for me? I was thinking of taking an intake manifold gasket and using that as a template to cut out a metal flange to attach at the engine and then weld on tubes to the flange. Then create a flange to attach at the carbs.
If you're going to go to that much trouble, I'd certainly rather have EFI than carbs...
Look into what ITBs are available from bikeland. When I built an ITB setup for my BMW 2002, I got some stuff right, and some stuff wrong. Some of what went well was lucky: 0.125" wall, 2" OD aluminum tubing had the same ID as the runners on the stub manifold I used to mount the injectors, and the correct OD for the jubilee clamps on the GSXR (eBay, uncertain on year, 1000cc) TBs I picked up.
Which brings us to item 1: Bike TBs that I've seen don't mount to a flange, they use a rubber coupling and clamp onto a tube. I believe the same is true for most bike carbs, though I'm not familiar with the latest stuff.
Item 2: Many of them are mounted on rails to keep them aligned, but you'll need to separate them and make new rails which mount them at the correct spacing for the Triumph's cylinders.
Item 3: Don't do like I did and just weld extensions onto the 'fingers' that let each TB actuate the one next to it (if that's how your TBs actuate). It was way too flexible, and resulted in no two cylinders having the same throttle opening. There are a number of ways to address this, just thought I'd mention how I screwed it up 
Item 4: ITBs provide less of a vacuum signal, so if you're going to MS (or other EFI) it, you might want to look at Alpha-N (throttle position) instead of MAP (manifold absolute pressure). Or heck, put the TBs in an airbox and run MAF. That being said, I think this is another area I fouled up: If I'd run a vacuum line from each TB into a small "plenum" and taken the signal from that, it might've worked. I cavalierly just T'd 1 to 2, 3 to 4, and then the halves together. I didn't even think through the order of the pulses, but I'm pretty sure the plenum approach would have been the way to go.
Better than listening to me, either find or wait here for someone who can tell you how they got it right instead of how they got it wrong...
Oh, another item: I'm not sure how much injectors have changed in the last couple of years, but most of what was available when I was looking were injectors meant to be pointed at the back of the intake valve, not "showerhead" nozzles meant to be mounted upstream. This meant that my DIY manifold arrangement needed to provide injector location, because it wouldn't have worked well to stick my injectors in the TB locations 8" upstream and around a bend from the intake valve. In my case, I lucked out with a tidily-sized CIS 320i stub manifold which also adapted my funny port shapes to nice round ones for my TB adaptors. You may want to look into what existing manifold bits might contribute something to help you simplify your fabrication task.
ransom wrote: Which brings us to item 1: Bike TBs that I've seen don't mount to a flange, they use a rubber coupling and clamp onto a tube. I believe the same is true for most bike carbs, though I'm not familiar with the latest stuff.
The GSX-R 600 TBs I am used to mount that way. I wasn't sure if that was all bikes.
i hear the ls1 has a nice intake manifold
ransom, could you make a bracket to hold the throttles above the head while some tube runs to pipes welded to a manifold flange?
im just curious from your experience if it would be an option
In reply to awdxboost:
I'm not sure I understand your question exactly... It sounds like you're suggesting separation of the jobs of mounting the TBs from the role of the manifold/adapter tubing?
I think I may also be getting lost in your use of "tube" and "pipes"... Care to specify materials? Draw a picture? Back away carefully from the guy whose previous advice mostly consists of "here's where you should do it any way but how I did..."
In my obviously semi-inept lack of expertise, I don't see why you couldn't mount them via some kind of bracketry built into the new mounting rails, but I don't understand why you'd want to as opposed to mounting by clamps to the manifold tubing as per normal...
http://www.triumphspitfire.com/carbchoices.html
http://www.totallytriumph.net/spitfire/carb_conversion.shtml
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