I know that there are mixed feelings on the relative merits of the backfire screen, but my question is a little more foundational than "pull it or don't pull it". Before deciding that question, I first have to wonder exactly what is the backfire screen supposed to do. I guess the answer to that question begins with what exactly is a backfire and how is it caused. After reading a bit, I am imagining a mini-wall of flames shooting through the carb and out through the airbox. If that is really what is happening, then I don't quite see what a wire mesh screen is going to do to hold it back other than generally resisting the flow of air backwards through the airbox. If that is the intent, then that really speaks to what an effective air flow reducer it is. It is no wonder that removing it would add a lot of airflow potential.

Anyway, not trying to stir up the "pull it or don't" controversy, but I would like to understand a little more how it works so that I can make my own decision.

Thanks,
Chris

 

I understand it as, it keeps the foam oil soaked air filter catching on fire if it were to back fire.... personally i dont wanna worry about a fire under my *** when im riding and i hear it backfire... which i never have herd ... kinda just like the 20$ re-packing cost, to protect your expensive pipe, its a no brainer to me... i would be very unhappy if my bike went up in flames.... we arent racing these bikes, how much could it actually decrease the performance? Thats one thing from the factory that i think ill leave there...

 

Eric, I agree that it is not worth the risk to take it out unless something else can be done to mitigate that risk. My question, though, is what does the backfire screen do in order to keep the filter from catching on fire? I would think that flames or heat that are sufficient to catch the filter on fire could easily pass through a wire mesh screen. Does the screen somehow disrupt the heat front or something?

 

it would block a short burst of flames, the holes are real small in the screen, so i would imagine that a fire ball would not be able to go through it, and the heat would not be there for enough time to ignite it just from heat... this is all my own thinking, and experience with fire... dont ask.... if i am wrong, someone jump right in.....

 

found some info for ya.....

One modification that many four stroke owners are talking about is the air box Mod. Most modern four strokes come from the factory with a backfire screen installed in the air box. The purpose of this screen is to break up sparks from a backfire that could start a fire. This sounds pretty important and it is, however there are other ways to control unwanted fire while also allowing for better air flow into the carburetor. No true race bike can afford the power loss caused by restricted air flow.

If you perform this modification, you will need to run a fire proof filter such as the Twin Air fire proof filter that comes with a special fire retardant on the inside to eliminate the chance of fire.

The stock back fire screen has several layers and is very dense, it restricts quite a bit of air flow, removing the screen will allow your bike to breath better and make more power.

You can simply cut the screen out of the frame but that looks pretty bad and is not a very professional way to go. WMR makes an a laser cut frame (Air Box Ring) that fits in perfectly to replace the factory back fire screen frame.

 

Yeah eric is right, I'm not an expert at all, but that small mesh screen actually takes up quite a bit of surface area, with No screen there would be 100% escape, mesh screen must block at least 50% of the flame and heat. I only know this because in my line of work when we ventilate a room with heat,smoke and fire, we ALWAYS remove not just the window BUT the screen too. The screen in question would act the same way. It holds back alot.

 

Great info guys. That makes sense. Thanks.

 

So, Twin Air makes a backfire "safe" filter for the KX250f, but not the KLX300/250s. Anyone have any ideas on the size/shape of the KX250f filter? Could it be used?? Any other genious ideas on mitigating the spark without the air restriction?

 

ive seen people saying that the K&N is suitable for this type of use... while i dont think its "fire proof" the fabric used isnt easily combustible.

 

The layers of fine mesh screen have 2 finctions. 1 is to stop sparks. But mainly the steel mesh will absorb enough heat from the flame front that it will extinguish the flame. A explosion have 2 components... a pressure wave and a flame on the leading edge of the pressure wave. If you can elminate one or both... the explosion is disipated.