vm or cv carbs?

[Steve]

Okay thanks but I do have cv style carbs, so I thought they needed the vacuum to function correctly.

There are actually TWO vacuum areas that are of significance here. The one that Rustybronco mentioned is the vacuum signal that is fed from one of the carbs (#3 on the VMs, #2 on the BSs) to the petcock to turn on the gas. That happens regardless of what type of carb, what type of air filter, whatever.

The other vacuum is the one you are wondering about here. There is a bit of vacuum required to lift the slides on the BS carbs. That vacuum is a result of having just a little bit of restriction in the air intake. Some of that is created by the size of the opening to the airbox, some is provided by the air filter material. That is why, if you change to pod filters, you have to make sure they are oiled properly to have a little bit of restriction, and also drill a larger hole in the slide so the diaphragms get a better chance of seeing that little bit of vacuum that is left.

If you still have the stock airbox, you can plug the vacuum port that feeds the vacuum to the petcock and use your manual petcock. If you don't plug that vacuum port, you will have a MASSIVE air leak for that cylinder and it will not run right.

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[rustybronco]

If you are interested in selling your parts carbs just let me know what you want for them. Thanks man

Not interested in selling "them". but, if you let me know which one you need, I will check and make sure it is the same body your '82 uses, then ship that carb body to you in exchange for your broken one. (they were given to me by Chuck Hahn @ no cost)

 

[neeko]

Look about half-way down on this page and confirm it for yourself. There is a nice list of what bikes require what sizes.

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hehe, Thats what I'm trying to figure out too!

It seems that for the intake orings and the years and models the 80 - 82 gs550 bracket is left blank and for the screws it makes no mention as well which really puts me in a very insecure iffy state

Thanks for the input

 

[jwegman]

hehe, Thats what I'm trying to figure out too!

It seems that for the intake orings and the years and models the 80 - 82 gs550 bracket is left blank and for the screws it makes no mention as well which really puts me in a very insecure iffy state

Thanks for the input

As I understood it, the page author most likely meant that they were the same as the item above it = 81-83 650's:

81-83 650's use 38mm O-rings and 16mm screws.
80-82 550's "

The safe bet would be to measure your existing screws and boot o-rings...?

 

[Steve]

It seems that for the intake orings and the years and models the 80 - 82 gs550 bracket is left blank and for the screws it makes no mention as well which really puts me in a very insecure iffy state

As I understood it, the page author most likely meant that they were the same as the item above it = 81-83 650's:
81-83 650's use 38mm O-rings and 16mm screws.
80-82 550's "

That's the way I take it, too.
Quote marks in a list mean "same as above".

.

 

[justintime_3]

Okay so I am a little confused. I have an 82 gs 850 with a broken carb. I am wanting to know if it will run right with the stock carbs minus a vacuum hose coming off of the fuel petcock. I will not be using the stock air box I will be using pod style filters and the exhaust is a straight pipe. So will this work or would it be possible to use the older style carbs that do not need vacuum.

 

[Steve]

It's the carbs that MAKE the vacuum, they don't USE it.

If I remember correctly, you are using a tank from another bike that has a manual petcock. Right? No problem. There is a vacuum port on the top of the outlet of carb #2 that used to go to the petcock. Cap that port with a rubber cap that you can get at an auto parts store. Before you install your pod filters, make sure you re-jet your carbs for the pod filters and the straight pipe. Depending on the brand of the filters and how straight the pipe is (it's actually based on restriction/backpressure, not the number of curves), you might need to go up 6 or 7 sizes on the main jet, maybe one size on the pilot fuel jet, raise the needle and adjust the mixture screws properly. Might help to drill out the vent hole in the bottom of the slides, as suggested by Dynojet with their kits. If you don't want to do a lot of guessing, just get a Dynojet Stage 3 kit for your bike. It has the added benefit of needles with a different taper, which will work better than simply raising the stock needles.

In other words, yes, you can use your current carbs, but you will have to do other things, too.

If you wanted to use the older style carbs, you would have to make some adapters, as they are smaller than your current carbs.

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[justintime_3]

Okay sweet Thanks a ton. I thought the carbs needed the vacuum line from the petcock to run. But I see now. I did purchase a jet kit of about 6 up Thanks for the help man I appreciate it. Just a GEE WIZZ question for you though. I do work at a machine shop so I could make the adapters, so I was just wondering if they would be easier to tune or if it's just gonna be more of a hassle than it's worth?

 

[rudy]

Just read the first page of posts, but thought I'd put in my 3 cents on the differences between VM's and CV's.

I've ridden both and I have to say that I like VM's better. My Yamaha's all have CV's, and the lag from throttle to GO is pretty bad on some. You don't notice it if you don't ride a VM bike. My GS1000 has VM's. Response is instantaneous. No lag at all. Not even from low speed to full throttle. It's not an engine size difference thing, because I've ridden my dad's FJ1200 with CV's. Same lag as all the other ones.

 

[waterman]

As I understood it, the page author most likely meant that they were the same as the item above it = 81-83 650's:

81-83 650's use 38mm O-rings and 16mm screws.
80-82 550's "

The safe bet would be to measure your existing screws and boot o-rings...?

I will confirm this info is correct. As an owner of both 550 and 650, the carbs are the same size and the intake manifolds are the same likewise. Order those with confidence.