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Carb "lingo"

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Could someone briefly explain the differences in the carbs available on our bikes, and some of the "lingo"? Such as:

VM
Flatside
roundside (RS?)
CV
smooth bore
square bore
SS
Are there more?

If one wants to use different carbs than what came stock, how does one determine which carbs would be a good replacement?
 
Re: Carb "lingo"

renobruce said:
Could someone briefly explain the differences in the carbs available on our bikes, and some of the "lingo"? Such as:

VM
Flatside
roundside (RS?)
CV
smooth bore
square bore
SS
Are there more?

If one wants to use different carbs than what came stock, how does one determine which carbs would be a good replacement?
Click to expand...

Assumning you know the difference between a vacuum operated carb and non-vacuum.

VM are non vacuum-carb used as stock from '76 up to 80 VM26SS, VM28SS for the 750-1000, smaller size for the 550.

Flatside? Do you mean flatslide? The big part that goes up and down in the carb and controls your venturi opening is the throttle slide, flatslide (sometimes semi-flatslides) have a faster reaction time.

roundside (RS?) You mean the RS series of carbs I think, made by Mikuni as go-faster carbs, pretty expensive sets

CV is the line of vacuum operated carbs used as stock on our bikes from '80 on (with some rare exceptions) CV32SS and CV34SS.

Smoothbore carbs are also aftermarket non-vacuum hop-up carbs such as the VM29 and VM33 Smoothbores, these have a very smooth bore (duh) which is good for the air intake.

square bore :?

SS designation means I believe that these carbs were fitted to bike models direct from the factory, the VM29 Smoothbores are aftermarket and don't have the SS part.

If you want to upgrade your carbs check out what others have used successfully along with similar mods as you're planning. But stock carbs can go a long way.
 
VM carbs were used prior to about 1980. They were smoothbores and the slide is controlled by the throttle, not vacuum.

Flatslides can be either CV type or smoothbore. Mikuni RS flatslides are serious carbs. They are smoothbores where the throttle raises and lowers the slide directly. RS flatslides have accelerator pumps built into them. You set them up to give an extra shot of fuel between 1/4 and 3/4 throttle openings.

Roundslides can again be either smoothbore or vacuum type. The VM series were roundslides.

CV type carbs use the throttle to open and close a throttle plate. Vacuum then raises the slide to open the venturi and raise the slide needle with it. They are great for meeting emissions standards and good fuel mileage.

Smoothbores don't have throttle plates, the throttle opens and closes the slides.

Square bore is an Edelbrock automotive design.

SS I believe is a carb popular for use on Harleys.

There are lots more, but they all operate on basically the same principal as already covered.
 
Slingshots were used on the second generation air/oil cooled Gixxers. They had a short intake tract angled to give a straighter shot into the port.
 
Billy Ricks said:
VM carbs were used prior to about 1980. They were smoothbores and the slide is controlled by the throttle, not vacuum.
Click to expand...

There is a huge difference between the generic GS carbs and the "race" VM29's.
IMGP0674.JPG


Th?s is a smooothbore. :D
Too bad i ruined my camera or else I would give a side by side comparison.

S&S = Harley carb, also used regularly on suck through turbo setups.
 
Hoomgar said:
That much I knew. But what are slingshot carbs?
Click to expand...

Slingshot carbs are a crossbreed, they are a semi-flatslide CV type carb.
The slides look like a half moon to try and strike a balance betwwen throttle response and smoothness, the slife is actually operated by vacuum as on a CV carb and they have a seperate throttle plate.
BTW these are also a semi-downdraft design as well, just to help confuse ya :wink:
Dink
 
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