The XJR is restricted by using narrower inlet rubbers. This becomes obvious when you measure the engine inlet diameter, 25mm and the rubber diameter 20mm. They cam be replaced with 25mm FJ rubbers or from alternative after market suppliers like Wemoto http://www.wemoto.com
Here you can see the difference between the two.
They will increase torque peak power by about 5bhp but across the range without any need for re jetting.
If you think that maybe someone has already done this mod to your bike, you can tell the difference in a couple of ways. The first is not easy to see, but the standard rubbers will have 4KG on the face pointing at the carbs, and the 36Y’s have 36Y on them.
The other way is by looking at the vacuum stubs that stick out of the rubbers. If they are pointing straight up, they are 36Y’s, an if they are pointing outwards at a 45 degree angle, they are standard.
1 ) Remove the seat and side panels, then undo the rear tank bolt with a 12mm socket
2 ) With Handlebars straight, raise the rear of the tank and remove the two breather pipes under the rear, remove the spring clamps by squeezing together and sliding them down the pipe before trying to pull the pipes off. They can be quite tight so watch your knuckles
4 ) Now undo the Vacuum pipe, squeeze the clip and slide it down, before removing the pipe.
5 ) Using long nose pliers release the clip on the fuel pipe and push it back, then push back the pipe, you may get a small amount of fuel come out of the pipe but as long as petrol valve is set to on and not prime that should be all
6 ) Now all the pipes are undone you can slide back the tank to clear its mounts and lift of the tank, once removed and put safely to one side, undo the three airbox bolts with a 10mm socket
Note: on newer models of the 1300 the inlets are longer than 36y’s so when you put it back together you’ll need to elongate the holes in the frame to allow the box to move further forwards and then the battery will need a little foam padding to make it snug again.
7 ) Using a cross head screwdriver undo the clips on the rear of the inlet rubbers where the carbs attach, note that when putting them back on later there is a notch in the top that lines up with a ridge in the rubber.
8 ) Now disconnect and remove the battery and slide back the airbox to release the carbs from the inlets, pull it back as far as you can as it’s pretty tight to get in to undo the allen bolts that attach the inlets to the head. Slide the clips you slackened off and let them hang on the carb outlets. This will give a bit more room to get an allen key in.
9 ) Using a 5mm allen key, undo the bolts holding the inlets to the head and slide out the old inlets working from the outside in.
10 ) Now just do it all again in reverse With the 36y inlets, make sure they’re nice and clean and apply a smear of grease to the mating face to give a good seal.
11 ) Now is a good time to balance your carbs.
The rubbers on newer black top carbs are longer by about 10mm. Replacing with 36y’s means lengthening the three air box mounting holes.
Alternatively you can have the existing rubbers bored out.
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