vm or cv carbs?

[bobbed750]

are there any advantages of running vm carbs over my cv's? i found a set for a reasonable amount, fully rebuilt...will they even fit my 81 gs550?

[Redman]

I can not fully answer that.

But can say that I understand the the VM carbs have the throttle cable activate the big slide in carb throat (on CV that is activated by a vaccum operated diaphram) as well as the throttle plate. And as such I wonder if the throttle cable attachment is something else you will have to look into if you want to install VM carbs on a bike that is expecting CV carbs.

I had alway thought that the CV carbs were an improvement over VM carbs. Most all models went from VM to CV carbs from 79 to 80 model year. (Steve may pop in here and point out the few exception and say I am wrong.)

A while back there was a posting of a guy with an 850G that he was asking what year it was,
some people said 79 because it had VM carbs (which is a valid reason to say 79), and other people said 80 or 81 becuase of other reasons that were also valid. And it turned out that it was an 80 that should have CV carbs but it had VM carbs that someone at sometime must have installed. So, it must be possible to somehow put a VM carb on a bike the expects VM. Someone suggested that they must have also had the rubber boots (and/or air box?) from the VM carbs (for some reason I dont recall) to get those carbs to fit that engine - but, again, that was for an 850G.

.

[hampshirehog]

They won't fit unless you change the cylinder head.

[twr1776]

Are your CV's bad or just needing a good cleaning?

I would be leery of a "rebuilt" set unless you trust the person doing it and they have done it before. Lots of bad stories here about poor quality rebuild kits being used and poor quality carb "rebuilders".

[Steve]

One advantage is that when you twist the throttle grip, they open up NOW.
One disadvantage is that when you twist the throttle grip, they open up NOW.

Huh? Although the slide action is quicker than the vacuum-operated slides on the CV carbs, the response of the engine might not be. If you open them too quickly, the engine will bog because there is no air moving across the jets in the carbs. The CV (Constant Velocity) carbs keep air flowing across the jets by opening the slide based on engine demand, not rider demand.

If you are racing, the VMs will give you better predictability. On the street, the CVs will give you better predictability (more-consistant response).

Many here will tell you that they are easier to tune if you want to go with pod filters and a header.

Will they fit? Not without some adapters. The CV carbs are sized larger than the VMs, so you would, at the very least, need new intake boots, but I don't know if the bolt spacing on the head is the same that would hold the boots.

That's my opinion, but you asked.

[tas850g]

There was a recent thread that said you can use an intake boot from a KZ to adapt the vm to cv on the carb intake side. I don't remember which kz model that was from

[Nessism]

There was a recent thread that said you can use an intake boot from a KZ to adapt the vm to cv on the carb intake side. I don't remember which kz model that was from

That thread was in reference to the large bore engines not the 550, although there may be something similar.

[old_chopper]

To not answer your question: I have a 1980 GS550L (well sort of) with the dreaded pods and drag pipes. I followed the cleaning procedures (even printed them off) and installed a dyno-jet stage 3 kit. After reinstalling and synching the carbs it runs like a Singer sewing machine. My point being don't assume these carbs are no good. Suzuki switched to them for a reason. I could not ask for my engine to run any better, least not without some cams, pistons, stroked crank, etc...

[justintime_3]

Okay so it's been a while since I have been on here. I am interested in this also. I have an 81 GS 850 I believe with the carbs that are vacuum controlled but I have a Kawasaki tank on it that the petcock does not have a vacuum hose on it. So I am wanting to put the older style carbs. You spoke of the ports on the engine being a different size. Does anyone know if this will work. Let me know Thanks. And yes I am chopping it Sorry. So I will be running straight pipes and pods.

[jwegman]

If you need to swap heads, I think I have a good one from a '78 550 (uses the VM carbs). I'm in the process of putting an '81 550 head on the '78 motor so I can use my CV carbs.

Now I'll have kickstart!

[landshark]

Cleaning and rebuilding your carbs isnt hard, and by the time your buy some adaptors to make it fit, you wouldnt be that far off the cost of the rebuild kits?
Plus you will know it is done properly.
My two cents.

[Steve]

... you wouldnt be that far off the cost of the rebuild kits? ...

Firstly, the o-rings and dip are a LOT less than the rebuild kits.

Secondly, don't waste your money on rebuild kits.

.

[landshark]

Secondly, don't waste your money on rebuild kits.

.

What do you use then?

[Steve]

If your float bowl gaskets are not torn, re-use them. If they need to be replaced, get them. Any of the online sources will have them for about $4 each or less.

For the rest of the carb parts, those of us here, "up over" use Berryman's Carb Cleaner Dip. Not sure what's available to those of you "down under". While waiting for the carbs to soak clean, order up a set of o-rings for the carbs, another set of o-rings for the intake tubes, if your bike has them, and stainless hardware for those tubes, all from cycleorings.com. Robert Barr, the owner of that little emporium, is a member here.

Typical cost of a "rebuild kit" is between $20 and $25. A can of "dip" is $20, and all the other stuff is less than $25, so, for less than the cost of just two kits, you can clean what you already have. An added factor is that the kits frequently have parts of sub-standard quality, so you will chase your tail trying to figure out why your "freshly re-built" carbs don't work right.

[landshark]

Thanks, that make sense.
My float bowl gaskets looked like old newspaper, so i bought kits.
We dont have berrymans, but i use methylated spirits and petrol mixed 50/50.
It works well.

If your float bowl gaskets are not torn, re-use them. If they need to be replaced, get them. Any of the online sources will have them for about $4 each or less.

For the rest of the carb parts, those of us here, "up over" use Berryman's Carb Cleaner Dip. Not sure what's available to those of you "down under". While waiting for the carbs to soak clean, order up a set of o-rings for the carbs, another set of o-rings for the intake tubes, if your bike has them, and stainless hardware for those tubes, all from cycleorings.com. Robert Barr, the owner of that little emporium, is a member here.

Typical cost of a "rebuild kit" is between $20 and $25. A can of "dip" is $20, and all the other stuff is less than $25, so, for less than the cost of just two kits, you can clean what you already have. An added factor is that the kits frequently have parts of sub-standard quality, so you will chase your tail trying to figure out why your "freshly re-built" carbs don't work right.