VM34s XS500

M

Marklorenzo

New Member
Hello everyone. I have a 1978 XS500 that I am working on. When purchased the carbs were complete junk. PO tried to remove pilot jets and drilled into them and destroyed them. So instead of trying to fix something that could probably not be fixed, I purchased a set of VM34s. The carbs fit into my carb holders snug at first, but it seems I have to really tighten the clamps down to make them somewhat snug. Not tight enough for rider comfort. Any ideas on what holders would work? Also, I purchased a 1 into 2 throttle cable from Carb Parts Warehouse along with a new throttle. I installed cable and it seems as though I do not have enough length on the carb end for full push and pull. Same at the throttle housing, seems to be getting stuck or not enough push pull for full movement. I can get the carbs to sit at half throttle open and close no problem, but no full range. I barely had enough room to attach cable to slide. Any ideas on this?



 
Ah. Something I have a little experience with.
1) I used worm and screw type hose clamps, like for a radiator hose on a car, to secure my VMs into the stock boots. This was strictly because I was being lazy, as you can get all sorts of carb boots from places like Sudco, as long as you have the proper measurements handy, ie. bolt spacing and orientation, and inlet diameter. My solution isn't ideal, but it works.
2) So-called "universal" parts universally don't fit ANYTHING without modification. Those cables may work with help, but if they don't have any slack, and you only get half throttle at the carb when your twist-grip is maxed out, you most likely need a twist-grip with more travel. The cables that came with my carbs worked fine for me, so that's my best guess. Not fact. Since you mention you bought a new twist-grip as well, I'd start there .
3) 34s are pretty big carbs. I would have for with 30s or 32s ( well.... Actually, I did go with 32s....) , but what's done is done.
Good luck!
 
i make up those cables all the time for my carb kits

if you need yours modded and cant find anyone local let me know

try some of the dirt bike people they usually have the stuff to fix it
 
Hey Mark- I have a few of these bikes, the throttle cable solution is straight forward, you will work that out without worries.

Now mounting the VM34's is more of an issue. The VM34 OD is 40mm on the head intake side.
The intake carb manifold was made for the stock Mikuni CV (BSII ) carbs are that have a larger mount flange at 42mm OD. That does not seem like much, however you will not be able to "crank down" enough to get a good seal and secure the carb with the metal shroud in place that fits over the rubber intake manifold ( assuming the filter end is just hanging there and no longer supported by the stock airbox boots. You can crank down on a clamp with the metal shroud removed, however you would be inviting boot failure, and soon.

On aftermarket intake manifolds ... as two-smoker mentioned, nothing made out there is even close and the XS500 has an added challenge : the carb side is obviously round, however the head side is unique in that it is OVAL , matching the oval intake port. Using anything other than a perfect match to the intake port would absolutely kill flow and performance..

There is a group of very experienced XS500 riders on a model specific forum. You can find some examples there of what others have done:

http://www.xs500forum.com/
 
Of course I would forget something.... I used a 1mm thick piece of heat-resistant nylon sheet from my work as a bushing around my carbs to take up that extra space... You'll see a bit of green in the picture where I fitted my carbs. That's the nylon. Thanks for the reminder, dean!
 
So are vm32s a better option for me? I'm so lost at what to do about these boots. I have searched the xs500 forum. Does not seem very active. I'm not too worried about figuring throttlw issue. More of the carb boot problem.

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If you just browse as a guest on the XS500 site, you will not have visibility into some technical sections that are member-only pages. Join the forum, introduce yourself, and then post the specific questions you have... The experts of the group will respond to with information and recommendations. It may not be that active of a site, however it is a make/ model specific site and the members there collectively have all of the information you would ever need. Do keep in mind that it is not a "help desk" and your participation with detail etc.. dictates the quality of responses.

IMO ...On an otherwise unmodified XS500 engine, I would say 32mm are the correct carb.
 
Well, I made mine... The important thing is the thickness and being heat resistant, as well as not letting air past, so you could use pieces of a tin can if they work. Anything soft enough to conform to the grooves in the carbs and not leak, as well as not melt. Silicone intake hose, maybe? There can't be a seam, because that will let air past. Hell, I suppose a rubber o-ring could work...
 
I did call sudco about boots just to see what they had to say. They have 70 mm bolt spacing boots for vm34. But they want 85 $ a piece!!!!!!


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Marklorenzo pm me the intake spacing on your head i may have a spigot around that might work
 
Remember, on the head side it is OVAL to match the oval intake ports .... If the boot does not match up to the intake port, you are killing flow .... ( there is a reason we port and polish our heads, installing a boot that does not even match up is the extreme opposite of a performance mod ! )
 
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