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Carburetor Vacuume Hoses

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I finally got my replacement carb from Kawasaki and there is a slight difference between the original OEM carb and the replacement OEM carb. 

The original had a single Vacuum hose that ran up under to the gas tank and connected to a part I am unfamiliar with. 

The replacement has two connections for vacuum hoses. I ran the first one to the same hose as the original. But I am unsure of the proper way to deal with the second. So I just capped it with a rubber plug. 

Without the cap in place the idle leaned out and the bike couldn’t maintain idle without the choke on. 

With the cap in place idle becomes extremely smooth with a noticeable loss in low end power. 

Im not really sure what to do here. 

Photos: new installed carb with a red cap over the second line. 

Original, damaged carb that only has one vacuum line. 



Edited by Dead_Eyes

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I reckon the red capped one is a a homemade hot start.

you could run a line from it up to handlebars and place a tap on it, with another piece of tube running to a filter to keep dirt out.

when u crash and bike is hot, open tap till its running again, then close

i did something similar on my 300 but ran the line into inlet manifold

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We should have the same bike, 2012 KLX250S, bought mine new so I know it is factory for what is sold in Colorado. I took some pics.IMG_3975.thumb.JPG.0463c6308bf01cb51057bb98ef17e02d.JPGIMG_3977.thumb.JPG.84fa75520844cba84f3cbc623d7e68eb.JPGIMG_3978.thumb.JPG.ea2f76c465b8cca3088d02c500106849.JPG

The top vent, black hose, goes to an emissions device that vents excess fuel vapor back into the gas tank eventually.

There is a vent on each side of my carb that is about a foot long tube at the lower rear shock mount, both tubes are clear.

The right side has a vent just above the idle screw tip that goes down towards the ground, and you can see the top black hose going to the emissions.

On the left side view the other vent is just beside the choke shaft,and it goes towards the ground.

The black tube on the left side view goes to the fuel petcock.

I have heard some stories of the length of vent tubes effecting venting, i.e. uncapped it behaves differently than with a 10 inch tube, I guess it would have some restriction with more hose. I would just make vent tubes a couple of inches below the lower frame tubes and case. Mine go behind the carb and route through the swingarm opening.


Edited by kdxyardsale

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Ok I originally had the same carb as you on my 2012. The one Kawasaki just sent me is identical except for the top vent hose. It has connections for two hoses. 

My guess is that maybe later year Klx’s make use of that second line. And our carbs have been superseded by this new, very slightly different design. 

The line from that emissions device pulls a vacuum so after talking to a Kawasaki dealer today, plugging the second line with a cap it was proper procedure. 

-Here’s where I was screwed up. 

I recently installed a big gun exhaust and broke my carb while tuning it... so when this new carb came in. Of course it would be running lean from the added airflow of a new slip on. 

To compound issues even more I had an air leak where the header pipe meets the slip on. 

So all in all, air leak fixed, and the fuel/air screw richned up its at a very stable warm idle of 1200rpm.  

Your photos helped me confirm that I wasn’t going crazy about the new design being different. 


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Excellent, I know some of the California models also have an emissions can or canister guys have modded out, maybe that port is part of it. Glad you got it fixed.

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