Mikuni VM34 Carbs

**James England** · 02-19-2014, 06:34 PM

Originally posted by D0wn5h1ft

Has anyone tried a modern replacement for our carbs like a set of VM34's? I see Mikuni VM's on all sorts of bikes nowadays that are being rebuilt, especially for those models that stock carb parts are impossible to find. I'm assuming they'd have to be jetted appropriately for our bikes which would take some tuning but with a brand new carb body replacement parts would be much easier and cheaper to find.

Amazon.com

http://www.amazon.com/Mikuni-Round-Series-Carburetor-VM34-168/dp/B000GV8QAO/ref=sr_1_1?ie=UTF8&qid=1392852348&sr=8-1&keywords=mikuni+carbs

Amazon.com

http://www.amazon.com/Mikuni-Rubber-Mounting-Flange-M-VM34-200K/dp/B000WJC9T4/ref=pd_bxgy_auto_img_y

I was thinking about getting a set of 4 of these and they even come with a matching set of carb boots! For ~$400 I think that it may very well be worth the investment.

Parts for the OEM cv carbs aren't difficult to find though....

**D0wn5h1ft** · 02-19-2014, 06:47 PM

Originally posted by James England

Parts for the OEM cv carbs aren't difficult to find though....

I guess but I'm speaking more to the general condition of these old, out of production carbs. Diaphragms are very expensive, carb boots are $100, broken float posts, broken off idle mixture screws, leaky throttle shafts...the list goes on. I'd really like to see if there's a way to update the 30 year old carb system without going fuel injection.

**motoman** · 02-19-2014, 07:23 PM

Originally posted by D0wn5h1ft

Has anyone tried a modern replacement for our carbs like a set of VM34's? I see Mikuni VM's on all sorts of bikes nowadays that are being rebuilt, especially for those models that stock carb parts are impossible to find. I'm assuming they'd have to be jetted appropriately for our bikes which would take some tuning but with a brand new carb body replacement parts would be much easier and cheaper to find.

Amazon.com

http://www.amazon.com/Mikuni-Round-Series-Carburetor-VM34-168/dp/B000GV8QAO/ref=sr_1_1?ie=UTF8&qid=1392852348&sr=8-1&keywords=mikuni+carbs

Amazon.com

http://www.amazon.com/Mikuni-Rubber-Mounting-Flange-M-VM34-200K/dp/B000WJC9T4/ref=pd_bxgy_auto_img_y

I was thinking about getting a set of 4 of these and they even come with a matching set of carb boots! For ~$400 I think that it may very well be worth the investment.

Manual slides and 4into1 'gang' cable...........would'nt say that's exactly modern

.

**D0wn5h1ft** · 02-19-2014, 07:29 PM

Originally posted by motoman

Manual slides and 4into1 'gang' cable...........would'nt say that's exactly modern

.

Yeah...I might getting stupid again. It just seems like there are so many other replacement carbs for other motorcycles beside the OEM ones. I've read about people using flat-side but that sounds like overkill. The obvious answer here to "update" the fuel system is to attempt fuel injection but I'm not prepared to go gray over something like that.

**crazy steve** · 02-19-2014, 07:53 PM

There's multiple reasons why those would be a poor choice.... the two biggies are...

First, you'll need four throttle cables; one to each carb. These carbs don't have throttle shafts/butterflies, instead the slide has to be mechanically lifted for throttle opening. So you'll need some sort of 4-to-1 cable adaptor to connect to the hand throttle, plus a length adjustment at each carb cable for carb syncing. I've seen these installed in two-carb setups, but never four, so this will all be custom.

Second, these aren't CV-type carbs. These are a throwback design, best suited to dirt bikes or racing where the throttle is usually either open or closed. You'll have a terrible flat spot at most sudden throttle openings, maybe big enough at off-idle that the bike will just die. A CV carb will only allow whatever amount of air it needs into the motor according to demand (engine vacuum), on these it's all mechanical. To help eliminate the stumble, you need an accelerator pump on the carb which these lack.

This type carb was commonly used in the 50s through to the 70s, but disappeared on most bikes because of both performance and emissions reasons.

**James England** · 02-19-2014, 08:24 PM

For civilised road use, CV carbs are best and easy to use, flatslides are noisy at low openings and a bit of a handful. Not suitable IMHO for anything other than track. I considered then for the XJR and dropped the idea after a bit of research and advice. A refurb of OEM cv carbs is easy to do and diaphragms have dropped in price recently.. I did a set and transformed them to solid, reliable carbs.

**bikerphil** · 02-19-2014, 09:38 PM

I would try the FJ or Zrx carbs if upgrading, all parts will still be available for those styles and the spacing should be correct.

**TomB** · 02-20-2014, 01:39 AM

I've never tried them on a 4 cylinder bike but have a pair on my CB72 sprint bike, they work great without flatspots and pull from tickover with huge torque all the way to red line.

I'm not sure but think the first CB750's used these type with a cable splitter similar to mine but with 4 outlet cables rather than my 2.

As said, the carbs are difficult to keep in sync, I considered 4 flatslides for my XS but was thinking of linking them with a lifter rail above and one cable

Error page | eBay

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