As promised I took some picture of the small mod I performed on the backfire screen.
First remove the seat in the usual manner. (Two 8mm bolts, 1 on either side panel.)
Next remove the lid to the airbox. (Skip this part if you run with the lid off.)
Undo the wingnut securing the airfilter and filter cage. Remove the airfilter and filter cage in one piece. Remove the filter from the filter cage. (Assess filter and clean as appropriate.) Store filter in a clean plastic bag to prevent contamination.
You can now clearly see the backfire screen in place where the airbox joins the airboot.
To remove the backfire screen you need to remove the 4, 8mm nuts securing the airbox, backfire screen and airboot together in a sandwich. See photo below.


Once the nuts have been removed, you can remove the backfire screen itself. Once removed, cover the now gaping hole so as to prevent small rodents making a home inside your engine. (This photo shows the AUS spec KLX300 high flow airboot. Yours may look different if it's a USA model.)


Next you have to trim the screen away from the plastic frame that supports the airfilter cage. I used a Stanley knife with a new blade. Take your time and cut the wire as close to the plastic as possible, taking care not to leave any wire sticking out.


Once all parts of the screen are removed, tidy the edges. I used a small modeling file and some emery cloth. It's very important to make sure the edges are smooth and all protruding parts of the left over screen are filed flush.

Once you are happy with the end result, give the modified part a good wash and clean to remove all traces of wire and plastic. Refit the filter cage and make sure there is no debris in the treads of the wingnut. (I always perform a 'dry fix' before fitting any new parts.)


You're done
Refit all the parts as they came out. The tricky part is making sure the rubber airboot is sandwiched firmly between the backfire screen frame and the airbox. Take your time here as a secure fit is mandatory. You don't want any 'unfiltered' air in the engine.
Here is the final fix. Ready to add the filter.

 

Good write up. I think that the US setup is a little different with the mounting nuts. There are 4 mounting nuts holding the backfire screen in, but you access them from inside the airbox. You will also need an 8mm swivel socket to get to the one on the bottom. Some have also used a socket and vise grips.

 

Good job. That's how mine looks.

 

Nice job, great pics. So how's it work, notice any difference? Supposed to get better air flow, right? Is it enough to bump up your main jet or move the clip position?

 

Im on a #138 main anyway. Just gone down from a #40 pilot to a #38 pilot as she was a little rich off idle. I let you know how she goes.

 

I'm waiting lol.. Seriously, hows it?

 

I can't comment on jet size either. I did mine when I did the intial first set of mods and jetted acordingly.

 

Nice job. Very clean work.

Sure wish the stateside and Japanese models came with the high flow boot.

 

For those that asked, it made a difference. Added crispness to the entire rev range and throttle response was notable better. Seems to have made the #138 main jet now 'spot on'.

Posted for Barbz.

 

i just did mine and it was time consuming, i am doing a rejet so i was pulling everything out anyhow, once airbox is out its easy to pull apart and cut out the screen, getting all the loose ends off is the issue, filing and sanding not to damage the plastic cage, similar to gutting the MAF recommended for my turbo vw, any restriction removed is good, also get the K+N #KA1287 as i seen here, i never liked foam air cleaners