ZXR750R-K Race Airbox
This paragraph details how to fit an Airtech Ram-air Airbox to a K model bike.
I bought a secondhand Airtech airbox (which uses the tank as its lid) which the previous owner had extended with fiberglass at the bottom to accomodate the stock Kawasaki FCR floatbowls. Although I didn’t need this extension as my FCRs use the Racekit float bowls (which are shorter) the modification was nice as it gives a useful amount of extra space to work with.
This airbox is a one piece unit with the front air scoop moulded in with the rest. This makes it a little trickier to manouvre in place, whilst boxes with a separate scoop are generally easier to fit.
I found that to get the airbox to sit as closely as possible to the engine (so as to give the carbs some clearance) I had to modify the airbox several times by cutting, grinding and patching with fibreglass. Making the airbox to seal properly was not straight forward though, particularly around the carbs and also right at the back where there is a large gap to the bottom of the tank.
To get a good seal you need materials such as several types of foam, high modulus silicone and a useful adhesive foam strip I found in plumbers shops.
If your bike is equipped with the “Air induction system” on top of the cam cover then you will have to remove this and plug the holes in the cam cover as otherwise the system would be in the way of the air-scoop.
I made some alluminium brackets (slightly stepped to make sure the rad would not make contact with the bolts and also that the rad fan would still clear the exhaust downpipes) to lower the radiator to allow it to clear the Ram air scoop of the new box. I also modified the lower part of the fairing to make sure the airflow to the repositioned radiator was not obstructed by the bodywork.
To get more room to manouvre I also relocated the coils (see link)
To make a good seal around the carbs I tried many methods, in the end (following a tip from my good friend Brian Kelleher – Thank you sir!) I resorted to making a fiberglass adapter plate which could bolt on to the bolts that hold the carb manifold (bolted on top of them and NOT between them and the engine). I have then sealed the gap around the carbs with silicon foam glued to the adapter with high modulus silicone.
I have then glued foam of different thicknesses around the edges of the adapter. These have the task of sealing the gap between the adapter and the airbox when this presses on it. I cut out the portion of the airbox that mates to the carbs manifolds as this would now mate to the adapter.
I used some soft, but dense foam around the edges of the airbox to get a good seal with the tank. I had to use different thicknesses. At the back of the airbox I used a large piece of fairly hard foam to build up a ridge and I glued some softer foam on top of it to make a good seal with the tank
When the airbox is in place and the fuel tank is on, the tank pushes the airbox down and the various layers of foam around the edges of the tank and around the carb manifolds compress making a good seal.
I have used a longer hose to route the crankcase vent to the new airbox
I have made an air filter using wire mesh and a light cotton sheet cut to shape and bonded at the edges using hot glue. The edges are finished with soft adhesive foam to ensure a good seal. The lot is bolted to the inside of the airbox covering the air intake.
I have not blocked the snorkel holes through the tank. Instead I have used a couple of layers of round cloth and used some duck tape to fit them on each of the 2 tank spouts to filter air coming in from there. The snorkels then clamp them securely in place.
I have changed the Throttle housing and cables for a quick throttle assembly and used the appropriate cables. I had initially routed these cables to enter the airbox passing between the airbox upper lip and the tank on the right hand side. However further modification forced a change on top of which I found that the cables were snagging on the ingnition block and getting damaged. I then decide to change the routing getting them to pass to the left in the stndard way and going though the airfilter (As you can see in some of the pics above). With the airbox and carbs in place I had real trouble trying to reach the clamp screws to clamp the carbs to the manifolds. In the end I decided to remove the “choke actuating braket” (FCRs don’t have real chokes, but the Kawasaki ones have an enrichener circuit which I have disconnected). With that out of the way I could tighten the screws and even without the “choke” the bike starts fine, but you have to keep nursing the throttle at standstill until the engine has warmed up a bit.
I have also removed the fuel tap (using shut off couplers) and only run the reserve line. This way I can have a much tidier (and lighter) setup.
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