Kray-Z wrote: Atlamillias -
Now that I know it is a twin, and what carbs you have stock (a linked / paired set of Mikuni BS-34 CV's - CV means "Constant Velocity"), and what carbs you have new (individual, single pull cable Mikuni VM28's, which are a round slide "smooth bore" carburetor), I can more accurately answer some of your questions!
First - carb spacing is typically referring to the distance, measured center to center, between multiple carburetors when they are solidly mounted together in a set or "brace", as with most 4 - cylinder engine's stock carb sets and like your stock BS34's. The term "carb spacing" does not apply to your individually mounted VM28's.
Second - "smooth bore" carburetors refers to carbs that do not use a butterfly type valve to control how much air enters the engine intake port. If you look at the engine side of the BS34's, you will see a round disk (this is the butterfly valve) mounted to a horizontal throttle shaft with two screws that almost completely blocks the airflow through the carb when the throttle is closed. When you pull the throttle cable to wide open, the butterfly valve rotates, opening, thus allowing more air to flow into the engine intake port. Even at wide open throttle, however, the butterfly valve restricts airflow - some of the carb throat area is still blocked because the butterfly valve and throttle shaft can not get out of the way of the incoming air and this impedes airflow. If you pull the throttle cable of a smooth bore carburetor , like your VM28's, wide open, the needle slide (which acts as the "throttle valve" on this type of carburetor) gets pulled upward into the top of the carburetor and completely out of he way of the incoming airflow, leaving only the relatively small area of the needle itself to impede the incoming airflow. You can look pretty clearly straight through a smooth bore carb when it is at wide open throttle! This is the reason why a smooth bore carb allows an engine to make more torque and power than a butterfly valve carb.
A CV carb uses a butterfly valve and relies on a vacuum chamber above the needle slide to open the slide and raise the needle. The vacuum is created (and increased) at the inlet (air box) end of the carb when the velocity of incoming air increases as the throttle is opened and engine speed is increasing. A spring is used to push the needle slide back down when the throttle is closed, and there is no mechanical connection between the slide's movement and the throttle cable. The "CV" type carb can't be a smooth bore, as without the butterfly valve, the rider would not be able to control the amount of air entering the intake port. At a constant inlet air velocity (constant throttle opening and engine rpm's) , the position of the slide stabilizes (hovers), hence the name...
Third - there are two shapes of needle slides common to both CV and smooth bore carbs - round and flat slides. Both your CV BS34's and the smooth bore VM28's are round slide carbs. Round slides have been around longer and are better in most street bike applications than flat slides. Racers prefer flat slides because they can give quicker and more precise throttle control and performance. One of the big disadvantages of flat slides is that they are prone to "sticking" to the carb bodies when engine vacuum or even high intake air velocity presses them hard against the pathway they move up and down in. Unlike round slides, where there is usually a large spring that pushes directly down on the slide, flat slides rely on a mechanical linkage with an external spring to return the slides to the closed position, making the problem worse. That is why using flat slide smooth bores like Mikuni RS34's or TM33's requires the use of a push / pull throttle and cable assembly (or a very stiff slide return spring that would make holding the throttle open for long periods very tiring and painful). One cable opens the throttles (slides) like usual, while the other cable closes them. That way if the slide sticks, the rider can still force ably close the slides with the twist grip - much safer than having a run-away bike! A push pull throttle is likewise commonly used (and highly recommended) with multi cylinder (3, 4, or 6 cylinder bikes) round slide smooth bore carbs that are bolted together with a common throttle linkage between the carbs, as a set and used on a street motorcycle - for safety reasons.
Because your VM28's are individually mounted to the engine (and are cable pulled round slide smooth bores), you can only use a single throttle cable (split into two near the carbs), so the point of a push / pull throttle cable assembly doesn't apply . I would only advise that for street use on a bike with no more than two cylinders, however...and be sure the cables move freely and the slides snap back closed firmly when the throttle is released before attempting to ride the bike...
There were quite a few of the Twin 750 LTD's around my area back in the late 80's, but I didn't even know there was a CSR version! I would often see adds in the local printed classifieds that read "198X KZ750 for sale" and see an asking price far below what a GPz750 or four cylinder KZ750-Whatever was worth at the time. I would call, sometimes even go to look at the bike, only to find out it was a twin, never having thought I would / should have asked first.... 
Thank you very much for all of the information, it was very detailed! And it probably would have helped if i myself were more.... descriptive.
