Mikuni VM 34mm carbs

I, personally, don't have them, but my Brit buddies swear by them. They only use the 34mm and a single carb. 2 into 1. They build some hi-po bikes and love 'em. They also have duel carbs on their daily riders, 34mm. I asked about the 36mm and they told me it's not very useful on a 650-750cc engine. I have read somewhere that for a 36mm to really perform you need a bike that has a much higher rpm range then the XS or simliar cc can handle. Again, I've never used them, but have seen what a good, tuned set can do.
 
i have a set im going to puton my street tracker like lil bill said theres alot of people who swear by them that they are one of the best performing carbs out there for the xs 650. be aware of the jetting though mine came with 25 pilot 180 main and p6 needle that my not work for you.
 
The VM34 is a decent low-priced carburetor. It's popular because of price and the fact that it's legal on the XS650 for AHRMA racing, while flat slides are not. That particular kit is from Sporting For Less, flying under another label--that little pitch that the OEM carbs "will never be right" identifies them. The air filters are Emgo-type--the filter medium is a very thin layer of foam, they won't stop anything smaller than pea gravel. The mounts are flimsy, and I'd advise against using them.

One thing to understand is that aftermarket carbs leave the factory with only one set of generic components, and anything that sets the carbs up for a particular application is extra money. The generic needle jet for the VM34 is the Q-2, which is usable on the XS650/750 only in full-race tune under race conditions. The generic needle will yield very poor results as well. Apart from the slides, those are the most expensive components in the carburetors. SFL made a regular practice of sending out a few kits with proper components and many with undersized main and pilot jets installed to compensate for the fat generic NJ. That way when someone complained online there was always someone else to say, truthfully, "Hey--mine were right!" and serve as an unwitting shill.

If you want to do things on the cheap, buy a pair of generic carb bodies wherever and jet them yourself; a very little looking will turn up the baseline that I and others have posted dozens of times. If you want quality mounts, filters, and cables, get them from MMM at 650 Central. Or get Michael's full kit; what you'll save on shipping from 3 or 4 suppliers will fund the difference, and you'll get Michael's tech support too.
 
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Yes, that place is indeed, Sporting for Less under a different name. Click on the seller's name and read his profile, it's in there. Don't buy from them.
 
Wow, that's a little off the wall. I don't trust those people/companies that only use "stock" photos or catalog type photos. They don't seem trustworthy, but that's just me.
 
Those are indeed SFL's pics, complete with junk filters and mounts. Michael sends the carbs with sound baseline jetting and a tuning guide, but there's no such animal as a bolt-on aftermarket carburetor. Fine tuning is always up to the buyer.
 
I use them on my '78... took a bit of tuning (with my junk filters) but ended up jetting larger. get a set of jets and a set of plugs to read and spend a half day making comparason runs till you dial it in.... however, out of the box they should fire your ride.

I originally traded some Amals for them at a british bike show, but they proved too big for the triumph (500) so I put them on the XS.
 
Hello.

I´m seriously thinking of getting myself a pair of those VM 34. Seems to be a carb that make sense if your into tuning your XS.

There is this guy here in Sweden ( I guess you can find them all over ) that sells a special kind of slide that fits a stock VM 34.....and other sizes. It´s called "UFO-slides" as you can see here at the adress.

It´s suppose to be even better then a flatslide carb...mostly at the mid-range. About 205 USD each for those. Money back if your not satisfyed.

But maybe you could make these "Ufo,s" yourself with some JB that we all love, right:laugh:

http://www.braigasen.com/news.htm

/BigBoreSwede
 
Thanks for all the input. I have bought the kit and will see how they work. I don't mind re-jetting them. They will be much easier to R&R for jetting than the stock carbs, and they cannot be more of a pain in the neck than my stock carbs have become. Once they come, and I have put them on, I will let you all know how thing turn out. They say that the set are already jetted for use with a stock XS650, which is what I have. If they run a little richer than the stock ones did, that will be OK too. I have an 81, and it has always run the plugs pretty white. If they go a little browner that will be fine. Speaking of which... since they stopped leading gas, has anyone else noticed that plugs don't tend to brown as nicely?
 
The Thunder Products UFO's look like refined snake oil to me. They've been around for years, and you'll notice they're marketed and produced by a snowmobile shop with a Secret Scientist yarn to go with them. If the mod were that hot, you'd think you might see race tuners using them (they don't, by the way) or that Mikuni might be paying royalties to use the design (more money in that for the patent holder than in direct sales out of a snowmobile shop). I like new toys, and I looked into them, even bought a pair to check them out. You have to butcher the slides to install the things by regrinding the cutaway. The UFO's are collecting dust. Anyone who wants to ruin a pair of slides and wind up with a cutaway that's too rich for the application can PM me--yours with instructions for the cost of postage.
 
I don't have them but when I was looking into VM carbs I was told that they don't handle altitude changes as well as CV carbs.
 
I am not looking for any power boost. In fact, even if these carbs give me a little less power, but prove more reliable, I will not complain. I am not a "tuner." My bike is a rat. It is my every day, run around, ride to the store and load the saddlebags bike. It is ugly, and I can leave it anywhere. All I want is a reliable replacement for the present stock carbs. As I said, I have already gone ahead and ordered this set, so They will be coming to me one way or another. I'll let you guys know how they work out.
 
If you want reliable the stock carbs can do it once dialed in. Most of the time a PROPER cleaning and re assembly is all thats needed. A good pair will clean up nice and work fine if they are not worn from high mileage or someone else doing bad repairs during the last 35 years. The biggest problem is getting the jetting right once someone changes the stock air filters and or exhaust. Filters make a big difference and some with exhaust. For a daily rider the CVs work great.
 
Amen to that, TwoJugs! I get tired of writing it, but aftermarket carburetors are not a good solution to maintenance issues, and even if the original carbs have terminal damage (hogged out passages from enthusiastic cleaning, etc.) a rebuildable pair of OEM carbies plus every piece of brass you can think of to replace will set you back a lot less than the cheapest pair of new aftermarket carbs. The BS series carbs are more responsive to atmospheric changes, and it takes far more skill to install and tune aftermarket carbs than it does to service the originals.

Mike, do yourself a big favor. First, order a copy of the Sudco Mikuni Tuning Manual and print off a copy of the VM section of the 650 Garage Carb Guide; lots of tuning diagnostics in the Sudco book. Also print off Gordon Jennings' fine article on plug reading from www.strappe.com .Then as soon as you get those carbs, open them up and check the brass--all of the brass--against the baseline I've posted a hundred times or so, flush the carbs thoroughly to remove any left-over manufacturing debris, and check the float level.
 
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