Post deleted by Steve_Claus

i asked Doug Dubach about this "trick", what he told me was... in case the engine back-fired it could cause the air filter to catch on fire...the cage is there to prevent this...

OUCH! Seeing as how you sit on top of the air filter... it might not be a good idea to remove that mesh. Do you guys smell something?! It's Rat Racing's roasted rump! Hehe, :)

:) Both Doug and Rat are correct, Rat I already done did this One of the many little insider in the know stuff people do. It is obviuos this will create a Hail storm of answers, but hey thats what we are here for.

:D If it Can breath in, it gets the wheels to spin

I would NOT take that screen out. Every notice how most spark arrestors are a screen insert? Same theory. As for the weight ... thats an ounce or two I'm willing to deal with ... Keep that screen clean and air will flow fine ... I've seen the YOT bikes being maintained at Broome last year and they have the screens ...

I know people that have had a totaled out, burnt to a crisp YZF's from doing this...If you do it, find a way to mount a fire exst. :)


Please post when your bike catches on fire so we can say "told you so".


I totally disagree that the screen causes turbulance. If anything, it smoothes the airflow and distributes it over a wider area. The design intent is to prevent flames from escaping the airbox in a backfire situation. And, yes the bikes WILL BACKFIRE on occasion!!

Also, a swirling effect is DESIRED!! Look at the shape of the airbox intake area, it's designed to swirl the air. Swirling helps atomize the air/fuel mixture. Virtually every performance engine swirls the airflow to some degree.

I totally recommend you go and buy a new airfilter cage before your bike catches on fire.

There are documented cases of this occuring; we're not making this stuff up.

Ya and when in full race garb the Spark arresters are removed >>> Splain That Why BREEEEEETH

Also If you bike is backfiring through the carb then there is something more wrong here, Only occurrance of carb back fire is from an ill tunned bike..........

So also use a non flammable-non petroleum base foam oil for the filter.

Anyway I go to fast to start a fire if it does occur the mere speed I travel extinguishes the flame

:) All valid arguments though

Nobody has mentioned the mere fact that a slightly clogged air cleaner will collapse a bit and with out the screen, could easily end up in the carb, possibly holding the slide up. A guy that was parked next to me once at the track oiled his filter up while he was there, didnt let it dry all the way and it sucked most of the wet oil out into the engine and collaped the filter all the way the screen.

Just my $.02

I disagree. A well tuned bike can backfire through the carb if flooded. We've all crashed and flooded the bikes if you ride long and hard enough. All it takes is one backfire to do the deed.

I hope you guys have fire insurance on your bike. You're going to need it.

:) OK OK Chillin lets not get carried away here, RAT when the dicing is done and checkard has fallen, those that crash wil always be bawling. Hey Sparky, The only thing you need to worry about is when you do dump your bike, is not to do it in front of alot of people I love to laugh

Uh oh Somthings coming and I sure do dred it...

:D Its all in fun, I have ridden since I was 9, I have only seen one bone head ignite his bike, why ? I dunno lets just say a short between the seat and the handle bars

Screens ARE firewalls, try a test yourself.

Get some metal screen and put a flame from a lighter under it. The flames will not go through the screen! Try it if you don't believe me.

Of course the plastic will melt eventually if you expose it long enough to flames. It's designed to withstand a quick blast of fire such as in a backfire, not a continuous fire.

Ever seen a radial heater (either propane or natural gas)? They ALL have screens to block the flames! You light them through a small opening in the screen, too!

Race systems do not use spark arrestors as they are not required for most closed course events, expecially on tracks. However, they are required for most off-road events and most off-road national forests (actually probably all of them). Do they decrease power? Probably, but the intent is to keep a glowing hot piece of carbon from catching the forest on fire-far more important than a fraction of a HP. You don't have to worry about that on an MX track.

Also, do you think Yamaha would REALLY go to the trouble and expense of putting a screen on it if it wasn't required? If it made more power and was safe to NOT use it, why is it there in the first place? The engineers that designed these machines are a hell of a lot smarter than you think. Everything has a purpose on the bike.

I'm not trying to piss anyone off, I'm just trying to relay FACTS! The FACT is the screen is present to stop flames from catching the filter on fire. Even Dr. D has confirmed this. If you remove the screen, you risk fire. Period!

Well here's my two bits. Somebody correct me if I'm wrong.

The air filter and air box does not and should not contribute to the atomization of fuel and air. If you have "a swirl" of air going into the carb, you have problems. Mainly because a swirl is a disturbance of low and high pressure - a carb's worst nightmare. Note that you could make a case for swirl on a carb that uses a butterfly venturi or for FI. Different story.

For dirt bikes, (or high dust environments) what you do want is an airbox that distributes the air (umm...dirt) evenly around the filter. Then you want the air filter to clean it. And of course both should keep things like water out.

For road bikes, the airbox can also serve as a compression chamber, which takes us to the next stage.

After the filter removes any harmful particles, the responsibility for the remainder of the snorkel assembly is velocity. Straight clean (no swirl) air into the back of the carb. Hence the use of velocity stacks or better put, decreasing angles.

Then at the carb, the fuel and air atomization process begins.

Now back to filters and that screen.

First, an inlet backfire is caused when fuel in the intake system is ignited. An exhaust backfire is caused when unburned fuel in the exhaust pipe is ignited.

The only way this can happen is that a spark, or heat high enough to ignite fuel, has to be present. There's no heat in the intake system, so it has to be a spark, (well…usually).

The only way for a spark to reach the intake tract is for improper valve or ignition timing. In other words, you'll never get intake backfire on this bike unless you have an engine or ignition failure. Ie, a bent or dropped intake valve, tossed cam chain, failed CDI…etc.

If you did have a backfire, the flame and heat would be very quick and little damage would be done. However, worst case, it could be enough to cause a portion of a foam air filter to come apart and get lodged in the carb slide assembly. An actual fire could only be caused if there is a combustible chemical in the air filter, (which oil is not). Hence the reason for not cleaning the air filter with solvent or gas.

By the way, during my early days, I tried lighting an oiled foam air filter on fire, and it’s nearly impossible. Oil just does not want to burn. I have also had numerous automobile backfires that charred the F*@! out of a foam filter, but the filter never caught on fire.

So, with care to proper cleaning solutions, the chance of the air filter catching on fire is just never going to happen.

As for two strokes, it would be very difficult to get a flame or backfire past the reed valve unit. Not to say that it couldn't happen.

Now, as for that screen.

The screen, in my opinion, is there for no other purpose than double protection. It provides integrity for the foam filter. Worst case, some idiot may never clean the filter, or the engine could break down, causing the foam to get pulled into the system. For guys that keep their bikes in top shape, it's not doing us any good. Just like many other things on this bike.

Is it really slowing us down?

I doubt it. The surface area of this air filter is enough to satisfy a V8 engine. However, at very high RPMs, it may help to remove the screen.

Long time ago (in ThumperTalk years) somebody did a dyno test with and without the screen. The results were posted and little if any difference was recorded.

However, the output from some dynos is hard to read unless you get in close. Perhaps it's hard to conclude on exactly what the results were.

What do I do?

I remove every-other screen in the assembly. This way I maintain the integrity of the foam structure but leave it open enough in the event that there is any starvation for air. Did I notice a difference? Can’t remember. Besides, I changed too many things at once.

If you ever see me out at ClubMoto, come over and take my bike for a spin. Perhaps an outside opinion could help.

Breathe on!


OK Mcarp

My wife is really pissed, I did what you said now I have a four foot burnt hole in my front door at home. I took my Flame thrower to the front steel screen mesh door and it burned that down and put a big ol hole in me door. Firewall My Butt


OK - RAT (perhaps thats a referenace to your bike's condition or the condition it will be in after running long enough without the screen)I was using the exhaust spark arrestor as an example, and my example was correct in the theory of what the air filter screen does. All of the other reasons why the screen should stay in place are also valid.

Furthermore, Mr. I Build Race Motors, the air does need to "swirl" for the best possible atomization of the fuel/air mixture. If you ever look at a motor thats been ported the ports are clearly "cleaned up" in a circular motion with the porting tool, not just "ground" in straight lines - This is also done to promote a higher level or atomization of the air fuel mixture.

Every watch NASCAR or NHRA I would say they are pretty high performance "race" engines. I would also say that they backfire under certain circumstances.

In conclusion, when your bike catches fire, and eventually it will, please post here so that everyone telling you why you should have the screen in place has the opportunity to remind you of how many times in this particular post alone you were warned against this.

Charlie Fisher

Hey Fishie

You been dropped on yer head to many times chill out S-A

Not to get on Rat But

Proper language in Email and posts are not to use CAPS, that means you are yelling or pissed or baligerant or


Only slam was to Rat. I have no problems w/ anyone until they jump on some friendly advice.

Please hold the "fishie" names .. Fisher

The signal to noise ratio is sky rocketing on this site.

OK, OK time to get back on topic guys :)

I had read in MXA a couple of years ago about not removing the screen for back fire potnetial (yea, I know, don't believe everything you read :D ) and think I remember a post here at TT a couple of years ago about a bike catching fire :D I also agree, some extra ponies might be found with the loss of the screen.

It's great to debate ideas and have challenging discussion but, come on.......


we now return you, to your regularly scheduled program :D

Here is onefor you.

not only the fire thing but..........yamaha also says not to leave your choke lever on for more time than it takes to keep your bike running smoothly, becaus it COULD suck your buttterfly choke thru the carb into the motor.

If the big ol' THUMPER can suck a butterfly out of a carb.......I think it could surely suck a flimsy little foam filter right into the carb or worse yet pull a chunk off and go thru the carb into the motor! :) Bend a valve and stick it........punch a piston thru a valve break a rod and destroy a crank ! :D and your entire block/head and send crap into you r tranny and clutch!!! but you may be able to save your cams :D:D

[ March 27, 2002: Message edited by: THUMPIN' ROCK HUCKER ]

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