Yesterday I removed the blow back screen between the carb and air filter, might be a little lean but noticeably stronger from 4.5K through red line.

So far; Cam mod (removed ACR completely) rejetted with Keihin jets (N1TC needle jet, #128 main and #40 pilot), DG can, stock header, now the screen removal.

Ain't no power wheelies, I'm a big guy, but for what it is, it pulls very strong and 50-70 mph and I'm getting 55-60 mpg.

Great bike! I have 6 others all much bigger, but I really enjoy the KLX, reminds me why I started riding 45 years ago. Light on it's feet, zippy, comfortable.

 

I really need to do this mod.. Don't I ?

 

No idea what specific power increase it produces, but every 4-stroke dirt bike I've owned since an '84 XR250R...I think about 10 up to now...have required a one-step richer main jet when removing the backfire screen...everything else being equal, of course. With an aftermarket pipe/muffler and everything jetted optimally, as soon as I removed the backfire screen and made a WOT run, I could detect a small but discernable detonation from a lean condition. One step up on the main jet, and all was well. Of course this says nothing about a specific power increase, and it says nothing about how this relates to every other bike out there. However, increasing airflow that requires a richer main jet almost always translates to better performance. Obviously a dyno, very consistent 1/4 mile test times, or other such monitoring would answer the question, but I think it's pretty conclusive just taking the cue from the detonation and jetting. Since it's mainly a WOT area of performance, it's not one of those seat-of-the-pants deals that you can feel...like a pumper carb, proper pipe, proper jetting, and other such tinkering. It costs practically nothing but just a little time to do, so what the heck...give it a go.

 

Removing the screen is not exactly a walk in the park getting the screws out of the inside of the airbox was a bit of a scream, I cut the actual screen out with a utility knife, and then used a small drum sander to smooth the edges of what was left.

I replaced the screws that held the screen in the air box with some screws that had hex heads which made it a lot easier to screw them back in when I was ready to reassemble.

 

Well, since I'm the only one that rides it now days.. guess I'd better remove the screen and see what I get.. Current carb setup could use a little more airflow and is set for max increase off the screen removal.. I was afraid my son would wreck with some chick on back, catch fire, and I'd be sued for removing the screen... You know if it gives another HP up on top, that'd be close to 24hp and I'll be DONE !

 

Your mention of the possibility of fire was, as you know, the reason for the backfire screen in the first place. However, over many decades of owning bikes with the screen removed and riding with many other owners of bikes with the screen removed, I've never seen a fire occur in those bikes. I've heard and seen internet stories and pics of black smudges from backfires on the inside of foam filters in the worst cases but not an actual fire. In cases where you have a backfire in a modern motorcycle engine bad enough to cause a fire, it's probably accompanied by some serious fuel and/or ignition issues. Most bikes don't have adjustable timing for a goober to screw up, so severe ignition ignited fuel fires aren't at all common like the days of adjustable distributor controlled ignition. It's good to be safe, but the backfire screen may be more of a lawyer holdover.

 

Yep, I agree..

So guess I'll fire up the cutting torch and warm up the saws-all.. Actually I think ARL said he pulled the rear suspension n swingarm to get the airbox out..

 

I did the job just taking the seat off and removing the air filter.

 

Yeah, 1/4" drive swivel socket set allowed me to remove that screen mount without much heartburn. The bulk of the work is making a clean job of the screen removal, which also, wasn't that hard, just a little tedious.

 

I removed the screen and had the same results as others. It felt a little off and needed a bump in the main jet. It does flow more air, but I did see a yout*be video of KTM on fire due to this mod. I run a K&N so I feel a little better as it has a built in screen, might be a false sense of security. I pulled the airbox out and disasembled, made things easy.