The Kawasaki ZX-12R - Kleen Air Removal With Crankcase Vacuum Procedure



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Kleen Air Removal

With Crankcase Vacuum Procedure






This Write-Up has been prepared and written by 'Blitz' - of






Here are the steps documented to perform the removal of the Kleen Air system AND add the crankcase vacuum modification.


This is an alternative to the Muzzy Block Off procedure I documented on this site ( The choice is yours. The pros of this procedure are:


1)      It costs about  $5 to do

2)      The reed valve covers do NOT have to be removed. This is a major issue, because the two inner reed cover mounting bolts are almost impossible to get at with a socket due to how tight the clearance is. If you try to remove them without the radiator out, you will learn the hard way what I mean.

3)      This procedure can be done without removing the radiator OR valve cover heat shield.

4)      Claims of 0.5 to 5 hp have been made on this mod. I cannot dispute or prove those numbers, but I can tell you that a large number of race teams are running this mod. After a year of reading and studying and talking to knowledgeable people on this mod, my gut instinct is that it is probably good for 1-2 hp on the 12. But that is free horsepower, no matter how much, and you get rid of the backfiring by removing the Kleen Air at the same time.


Essentially, this modification removes the Kleen Air vacuum pump and routes the crankcase vent tube (which exits above the counter-shaft sprocket cover) to a tee installed between the Kleen Air reed valves.


This subject has been discussed many times on the site, but since we were doing it today, I figured we’d document it thoroughly while we were at it.


Credits: Green Mamba, Tenn12 and ZX12Richard (in order of posts chronologically) all contributed directly to these procedures. Richard was especially helpful the morning we did this mod by emailing us his pictures for reference, routing diagrams and going over things on the phone before we started.


These guys did the leg work and research and this is a conglomeration of those thoughts, ideas, procedures with a few tips we discovered while doing it.


06/01/2004: I have added some changes recommended by tslewisz, specifically:


1)      Clarify that a ⅝” adaptor not a Ύ” adaptor is needed.

2)      Add pictures and description for using a copper tee vs. a plastic one.

3)      Add pictures and part description for using PVC hose (optional)


We hope this helps the next person who does this mod!


- Blitz / Ergo Kinetics.


1) Parts List:


-         Four 1” screw style hose clamps.

-         Two ⅝” screw style clamps.

-         One 5/8” male to male connector (length approx. 2 ½””)

-         One ½” barbed insert tee (Home Depot P/N 851405), or three 1 ½”" pieces of ½” copper tubing and one copper tee

-         (optional) a few feet of ½” flexible PVC hose.

-         One bicycle handlebar end plug (rubber or soft plastic branched style preferred)


2) How to do it:



a)      Get the bike naked on both sides. Label the electrical connectors carefully and disconnect the left and right side electrical connectors and the fast idle cable on the right side. The throttle cables remain in place.



b)      This photo shows the left side Kleen Air reed valve cover outlined in green. Note all the connectors are numbered (on both sides of the bike) with bright blue 3m painters masking tape for easy reassembly. Use the ram-air intake for reference.





c)      This is the trick to saving a lot of time. You do NOT have to unbolt the reed valve covers. Note the green line pointing to the large screwdriver blade placed at the hose seat.




d)      And voila, it pops out. Do the same on the left side reed valve cover.







e)      This is the Kleen Air vacuum pump being pulled out of the left side of the bike after the above steps. Green circles the pump. Red points to the vacuum feed line which you need to plug. Do this now (plug the vacuum line). Shorten it if you wish, but we left it long and zip tied it just in case smog inspections become an issue. It would be very easy to hook this all back up in the unlikely event we need to.




f)        This photo above is the vacuum line (step e), after plugging and zip tied.



g)      This photo shows the plugging of the right side airbox port with a bicycle handlebar end plug. Silicone the plug in for a secure, airtight fit. Leave the factory rubber grommet in place. * The hose that was here is outlined in blue in caption (i), for reference. (The removed fast idle cable holder is boxed in yellow.)







The Crankcase Breather Pipe, is in here.





Just here.





The other end of The Crankcase Breather Pipe,

joins to The Air (frame) Box here.


Remove this end of The Pipe,

and join it to the The Pipe coming from the Reed Valve Tee








h)      Okay, here is where things seem more complicated than they are:


-         The yellow indicates were the original crankcase vent went on the inside of the frame up to and attached to the left side of the airbox. The red dot in the upper right hand corner needs to be plugged off.

-         The hose marked in purple used to be in the upper yellow line position. You need to pull it down through, and outside of the frame. Its tight and takes some time, but you can work it through. When you do it, the placement will be obvious – almost like Kawasaki intended it to go there…

-         The green indicates where the male to male ⅝” adapter goes in. Home Depot was out of ⅝” adaptors when we did the mod, so we used a Ύ” adaptor. It’s a very tight fit and the ⅝” adaptor is a much better fit. Secure the adaptor with ⅝” screw clamps..

-         The blue indicates the hose we reused from the original Kleen Air. This is the hose indicated in blue in the next picture.



i)        The above photos are (left) a 49 state Kleen Air vacuum pump and (right) a California style vacuum pump. Note that our donor bike today was supposedly from Florida, so don’t assume anything – it had the Cali emissions system. The Cali bike will have a purge canister sitting behind the rear cowl storage area that you can see easily between the plastic tray and the rear taillight.


The green line on the right pump (in the picture above) points to the purge canister bleed off. (CA only.)


Block this line off if doing this modification.


At this point, the purge canister is rendered useless.










j)        The above photos are of the tee, and matching up the tee to the stock Kleen Air reed valves. We had to cut off one barb section of the tee (as indicated by the green marks – look for the little skinny marks in the photo) because the flanges on the stock reed valve cover hoses have hard stops, and the tee will only go in so far.


The second photo above is a ½” copper tee. A few pieces of  ½” copper and a tee may be used.  The picture compares the assembled tee with the KleenAir can.  A ½” (non-barbed) tee is in the background.  The non-barbed tee is too small to work.



        k)     Here you see the finished product. Plug all the connectors back together, put the plastic back on, clean the bike, and go enjoy.  If you decide to use 1/2" plastic PVC,

                it will look like the following photo.



Blitz & Ergo.


Thanks Blitz and Ergo, awesome job.


This is an excellent contribution to            



My Opinion                                        


I'm not sure if this mod does anything for performance,

but it does stop the flames and backfiring from the exhaust

when throttling off, whilst using 'after market' exhaust systems.



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