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Discussion Starter #1
As I was preparing to replace my rusted chain with the new O-Ring I bought, I decided to do some routine maintenance.

I removed the air cleaner cover and found 2-3 ounces of water and a pile of rust.

As I was gently attempting to absorb the water and clean out the rust, I bairley touched the screen and poked a hole in it.

Anyone know a reasonably priced source to replace this screen and filter element?
 

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I can't help you with the screen and airbox however when I got my '06 I also did some regular maintenance and I also found a couple of ounces of water in my airbox but it hadn't caused any damage. I assumed the previous owner used a pressure washr to clean it up and that is how the water got there but I was not able to confirm if that was the case. Good luck getting your bike all cleaned up and detailing the airbox.
 

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Look up woven wire mesh on Amazon or other vendors. Even stainless steel didn’t seem too expensive, especially since you don’t need a window size. In light of the rust you found, stainless seems like a good idea. The stock screen looks to be molded into the body, so you’d have to get clever to install it.

When I rode in a lot in the sand, we all wrapped pantyhose material around our filters. I was amazed at the durability and if I needed more airflow I would just stretch it more. But you really need to inspect it often. Cheers
 
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I would just remove the rest of the screen....it serves as a spark arestor and is not necessary imo....Just be careful as you remove it as it wants to poke holes in your fingers.
 

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A spark getting through the carburetor, manifolds, and the breather?...highly unlikely. It's there to support the foam filter from getting sucked in and blocking airflow.
 

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Discussion Starter #6
A spark getting through the carburetor, manifolds, and the breather?...highly unlikely. It's there to support the foam filter from getting sucked in and blocking airflow.
That makes far more sense to me...
 
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Discussion Starter #7
I got my new O-Ring chain installed today. Went on without a hitch.

I’m still concerned about the condition of the screen in the airbox. There's a ton of stuff behind the screen, mostly rust and pieces of the screen. The screen appears to be permenantly attached to the airbox.

Any suggestions on how to get the stuff from behind the screen?
 
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I think it might be molded in place. If so I'd cut it out and give a super thorough degreasing and look into replacing the mesh with something rust resistant and installing it with something like JB weld putty. A friend of mine used it to make a boost bottle and it held up fine.
 

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It’s part of a removable piece. Mine was nasty, but cleaned up fine. I believe the mesh is molded into the piece. Removal of that piece was a PIA as there are screws or bolts that need to be removed from the back side. If the swingarm was removed or I had a lift, removal would have been much easier and my dog would not have witnessed my curse factor of 10. I can maybe get you more pics if you decide to tackle removal. Cheers
 

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A spark getting through the carburetor, manifolds, and the breather?...highly unlikely. It's there to support the foam filter from getting sucked in and blocking airflow.
You sound very confident and certain of this....Are you sure?

Of course it will prevent the foam or pieces of it from getting sucked into the engine but logic dictates that it has another perhaps more important function. There may be a reason why there is a gap between the metal screen and the filter itself. Why have the plastic filter support, a gap, and then a metal screen? Certainly either the plastic filter holder or the metal screen is redundant.... Why not just use a metal screen to hold the filter?

Furthermore if you have ever seen a single cylinder engine run with the high pressure side of the carb exposed...they sometimes will spit fuel in the wrong direction, particularly during throttle transitions. This may be caused by the intake valve moving about. This wrong direction fuel flow is highly likely to be headed for the sponge like foam filter where it may reside awaiting a highly unlikely misfire/back fire. If this where to occur after a tip over or otherwise flooded engine and the engine backfires thru the carb and fails to start altogether.....it could result in a small fire in the oil soaked foam filter. This has the potential to be a bad thing....

Perhaps I lead you down this path by my use of generic terms....Instead of "spark arrestor" I should have possibly suggested that it is a backfire screen and avoided all this confusion....I just googled backfire screen and it was very informative...I stand corrected!
 

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Discussion Starter #11
It’s part of a removable piece. Mine was nasty, but cleaned up fine. I believe the mesh is molded into the piece. Removal of that piece was a PIA as there are screws or bolts that need to be removed from the back side. If the swingarm was removed or I had a lift, removal would have been much easier and my dog would not have witnessed my curse factor of 10. I can maybe get you more pics if you decide to tackle removal. Cheers
Thanks, that helped.

So, I can either cut out the existing trashed screen and replace with something similar using JB Weld or epoxy or remove the part containing the screen by removing the swingarm to access the screws that are on the backside.

Or, use a lift? How dies a lift gain access?
 

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1...a spark in your carburetor might ignite the fuel there. Otherwise it would likely by cooled by liquid fuel.
2...a spark has as good of a chance past a spark arrestor as it does the complicated journey through jets to get to your air box.
3 ...the dominant flow of the airbox is into the carb. Like the dominant flow of the exhaust is outward.

Also the XR250L has no mesh screen just foam. Neither do the motorized bicycle 2 strokes or 4 strokes I've worked on.

TW has just a loose piece of foam with no frame that is suspended in front of the mesh. The XR has a rigid foam with a frame built into it.


I just googled backfire screen and yes that's what it implies but makes no logical sense. Especially if you think about what happens in a carburetor.
 

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Glad to see you googled that. Debate/discussion often leads to learning for the parties involved. I am no expert on any of this stuff and have been wrong/misinformed on many occasions. I am somewhat certain that I am right here, but I would welcome rebuttal if you or others have some insight on this topic that concludes otherwise....I have gained an incredible amount of knowledge from forum members and continue to do so....
 

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Glad to see you googled that. Debate/discussion often leads to learning for the parties involved. I am no expert on any of this stuff and have been wrong/misinformed on many occasions. I am somewhat certain that I am right here, but I would welcome rebuttal if you or others have some insight on this topic that concludes otherwise....I have gained an incredible amount of knowledge from forum members and continue to do so....
i agree with you. once a motor has lots of miles, the valve train can be worn and sloppy enough to cause a backfire through the carb and up into the air filter
 

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A lift puts the bike up higher so you can work standing up versus on your back on the ground. In this case, it would have also made it easier for me to see the screws I was trying to blindly remove. Cheers
 

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I'm always open to the possibility of being wrong. Even when all logic dictates otherwise. What matter most here is that Tjmay gets the info needed to deal with his situation. And if we all learn a little something then bonus.

Looking at pumper carbs and not sure where else the manifold tube intakes from I could see that being a candidate for backfire protection...but otherwise it seems to be impossible for flame to travel that way through the carb. If so I'd be concerned about it traveling up the gas tank. But then again liquid gas isn't flammable it's the fumes. Removing the screen is very very common and those who instruct how to do it include a disclaimer.
 

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Discussion Starter #17
What matter most here is that Tjmay gets the info needed to deal with his situation. And if we all learn a little something then bonus.
I’m a member of several forums and it is this attitude that sets you guys apart from the rest!

Thanks to all for your input...
 

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Discussion Starter #18
In view of the many comments here about the screen not being just a surface to support the othjer side of the air filter element but a backfire screen as well, I'm still pondering what to do about the condition of this screen.

Does anybody have the pages of the service manaul that explain the removeal proceedure of this puppy?
 
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Just my 2C, upon replacing my 2017 stock air filter with a Uni aftermarket, I didn't see any metal screen in the airbox. The 2017 has a plastic skeleton frame which backs the filter to keep it from being sucked into the carb throat.
 

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Maybe you don’t need to replace the screen after all. But for those who need or want to remove the piece, here are some low quality photos of the screw that is hardest to get at. I probably made it sound worse than it is. If I can do it, anybody can. Cheers
 

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