Hello and Motorcycle Throttle Body Selection

[nathanh]

As this is my first post Hello to you all.

My project bike is, or will be a 1260GSX Katana (Suzuki), for those of you who aren't familiar with it, she's got 1982 Air cooled Engine.

As far as EFI goes I'm still in the early planning stages, but I need to select throttle bodies soon to see how much room to play with as I'm finalising the engine mounts and frame bracing. So at this stage I just want to confirm a few things I've gleaned scouring this forum and the manual.

The intake ports on the engine have centres of 78-98-78 with a 40mm OD, which would make the Bandit 1250 a good fit with centres of 79-100-79 (OD-41mm) or even the GSX1400 with centres of 71-112-71(OD-47mm), although getting rubbers to fit the miss-matched ports might be an issue.(note: these figures were given to me by ebay sellers so might not be entirely accurate)

A lot of people opt for the GSXR-600 throttle bodies for the GSX engine, from what I've read pretty much all Suzuki TBs have the same output capacity, but it still concerns me using TBs from an engine half the size of mine. Am I worrying unnecessarily. I would also like the fuel system to be able to cope if I decide to up the power of the engine through a turbo or such like at a later date.

So I guess my question is; am I on the right path and if not what should I be considering?
Any other advice in planning my set up will also be gratefully received.

Many Thanks

[SQLGUY]

My setup was completely different (http://residentialcolorado.com/SECA_750i.htm), but as to the size of the throttle bodies, I'd look at the venturi size of your existing carburetors. If the GSX600 TB's are about the same as your current carbs, then you really should be fine, especially since the TB's only flow air, rather than air+fuel.

While the 600 may be a much smaller engine, its HP is probably not too far off what your 1982 1200 makes. I'd be most concerned about being able to effectively connect and seal the TB's to the intake ports.

Another thing to consider is that, depending on how the TB's are ganged, they may well be adjustable as to centers. Your best bet may be to find TB's whose ODs fit your stock intake boots, and then do whatever work is needed to their ganging to adjust their centers to line up.

There are also some success stories over on the main MSefi forum that relate to motorcycle conversions.

Cheers,
Paul

[nathanh]

Thanks and for the link I've just read it and I think It's convinced me to go for a fuel only set up to begin with ;)

You're right I'll have to make sure I can get the right inlet rubbers for any set up I choose and I expect anything that isn't close to the original carb OD is going to be tricky to source.

The Carb OD for the Katana is 42 mm which means the Bandit 1250 could still be a good option as they are 41mm, but I guess equally they could stretch to the GSXR600's 44mm. Decisions, decisions????

Time to trawl through the success stories again methinks

[pommie02]

the early gsxr 750 throttle bodies are easy to adapt, the hardest thing was to get a fuel rail made

[nathanh]

Thanks pommie02, according to the post about the various throttle bodies they list the GSXR750 as having a OD of 54mm, which rubbers did you use?

[pommie02]

the suzuki ones are no good, because they bolt straight on to the head, so you would have to get some adapter plates made.
i used my original rubbers and made the holes bigger to accept the throttle bodies