The GT750 was a 3 cylinder motorcycle with a 2 stroke engine.  It has no need for a TEV valve, and the jetting requirements are far different than the Savage.

You could go crazy trying to sort though the different variations of Mikuni carbs, as they are also used on snowmobiles....and I suppose could be used on any engine.  

Sentimental moment: This forum is an endless source of wisdom. Much appreciation. Thanks guys

I believe Dave is  right our stock carb works fine on the bike ,with a bit of work it can become better, changing jets ,the white spacer mod ,are both good examples of what can be done, I've also gone to a tuned intake 18 " long ( that you can't see as it's inside the stock air box), and drilled my vacuum ports in the carb slightly oversize( which kills most of the throttle lag normally seen in CV carbs) .That combined with a Dyna muffler ,puts me at an estimated 34-35 hp , Speeds in the 60-72 and 80 -92 range in 5th gear, gains can be found elsewhere (lower gears) due to increased EV of 4% and 7% ,that are dependent only on rpm. With an internally stock motor,a top speed a few ticks past 90,with a minimal investment of time and money the bike runs as strong as I could hope for.At rpm ranges outside of 3822 to 4686and5096 to 5860rpms , the motor runs as normal ,running at 55 or3503rpm ,I'm getting 48 mpg that's been my norm for years.

I contacted the guy who posted the old suzuki carb guide link I listed above. I was asking him about the differences between the BS40 and BS40SS. He seemed like a knowledgeable guy, so I'm posting his email response to me, including some pics he sent.

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Hi Andy,

No idea what the nomenclature means.  They have VM for round slide, BS for CV carbs with round slides.  They added SS on the end of some BS carbs and on some VM carbs too.  Some BS(T) carbs have flat slides just to confuse the issue.

The 40 refers to the carb throat diameter and in the case of GT carbs it is the outlet diameter.  Carbs on a GT750 have a ramp in the throat which is probably there to increase gas speed through there so that the slides will lift.  4 strokes have stronger suction than a two stroke so the 2 stroke needs ways to speed up air flow especially at low speeds.

early 4 stroke BS series carbs tend to have a more open throat and use "bleed" type emulsion tubes/needle jets compared to the Primary type in a 2 stroke. In Bleed type, air is mixed with fuel to create an emulsion ie smaller droplets to burn better. Remember that liquid fuel does not burn.  Odd but true. It is the vapor on the surface of each bubble or drop od fuel that burns and here's the trick.  For the same volume of fuel, smaller droplets have greater surface area and therefore burn faster and more completely.  That's also why modern fuel injectors have more (smaller) outlet nozzles to better break up teh fuel into smaller droplets.

So back to your bike and 4 stroke BS carbs. A version of those have been used on most 4 strokes from Suzuki for years including GSXRs and most other street bikes.  GSXRs use a flat or semi flat slide for better throttle response.  Most earlier carbs use a round slide with rubber diaphragm similar to a GT750. That way the slides rise as gas velocity increases and that makes for a much smoother road bike.  Almost the same idea as modern fly-by-wire but without the computer control.  The slide rises in relation to engine load, so it adjusts to the engine needs.

Attached is a cross section of an XS650 carb and you can see the difference in the throat under the slide.  That same basic design is used on many Suzuki and Yamaha twins from that era.

Yours has a few differences.  The choke (enricher) is the same idea but is cross mounted rather than vertical and it appears to have an accelerator pump on it.

Do a quick google search for Suzuki Savage carburettor and you will find a lot of useful leads.  I'd also recommend getting a Factory Service Manual.  It looks like there are some downloads and maybe one on ebay too.

Cheers

Would like to help, but have problems of my own,  like trying a 36mm  Dellorto .