Removing Backfire Screen


55 replies to this topic
  • Joe_Jet

Posted October 16, 2004 - 03:32 PM

#1

Has anyone else done ths? How do you remove the screen particles that are embedded in the plastic cage? Does someone make an aftermarket cage?

Thanks,

  • Satch0922

Posted October 16, 2004 - 03:52 PM

#2

Twin air makes one....or you can get the YZ250 cage from Yamaha.

  • grayracer513

Posted October 16, 2004 - 03:53 PM

#3

This has been done, but I don't recommend it, because some of those little bits of wire you mentioned could work loose and get into mischief.

Use a cage from a YZ250R (two-stroke). They are identical except for the lack of a screen, and cost about $28 at your dealer.

Be advised that 4-strokes are quite capable of shoving melon-sized fireballs out of the mouth of the carb. If this happens you could set fire to your air filter and then your bike(particularly if you clean it with gas or use a flammable oil to oil it with), or burn a hole in the filter through which the real crusty demons can enter. To avoid this, use an air filter element that specifies its ability to be flame retardant.

  • YZ250F_Rider

Posted October 16, 2004 - 07:11 PM

#4

In all the years of posting on here there has only been one instance of a backfire that caused the filter to catch on fire. I run a twinair backfire filter just in case. I would hate to be the second incident.

Cut the rear wall of the airbox down flush with the fender while you are in there.

  • Chipstien

Posted October 16, 2004 - 08:20 PM

#5

Is there something to be gained from removing the screen? That can hardly cause a restriction. It is amazing how far some will go to get a 1/32 of a horsepower increase. :cry: :cry:

  • grayracer513

Posted October 16, 2004 - 09:06 PM

#6

True, it isn't common, but as you said, you wouldn't want to be one of the chosen few.

Frankly, the possiblity of holing the filter and not being aware of it for two weeks worries me at least as much.

  • Rich_Rohrich

Posted October 16, 2004 - 09:08 PM

#7

Is there something to be gained from removing the screen?


Not in this case.

  • grayracer513

Posted October 16, 2004 - 09:13 PM

#8

Is there something to be gained from removing the screen? That can hardly cause a restriction.


I tend to think not, on a 250, but possibly yes on a big bike. I suppose only a flow bench would really tell you. But, if you take the screen out, and find the bike suddenly leaner at full throttle, you have your answer. That can only mean a pressure drop across the screen.

  • Chipstien

Posted October 16, 2004 - 09:30 PM

#9

Is there something to be gained from removing the screen?


Not in this case.

So what is the point of removing it :cry:.....

  • YZ250F_Rider

Posted October 16, 2004 - 09:57 PM

#10

Is there something to be gained from removing the screen?


Not in this case.

So what is the point of removing it :cry:.....


Good question. You should ask the pro level guys why they dont ride with one. I doubt that it's because they cant afford it. :cry:

Of course you can gain hp by removing it. It's a wide open gain in hp, not down low. But you need to cut the rear wall of the airbox down flush with the fender to see any real benefits. And of course all is wasted without a good high revving pipe. Always think of the intake and exhast as a system. They depend on each other, and affect each other.

As for gaining 1/32 of hp... It amazes me more some dont believe, and that some dont even care.

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  • Satch0922

Posted October 17, 2004 - 05:17 AM

#11

you know guys it's not about one mod changing the world ...it's about several mods working together for the betterment of the world :cry: :cry:

  • Rich_Rohrich

Posted October 17, 2004 - 07:30 AM

#12

Good question. You should ask the pro level guys why they dont ride with one.



After a lengthy development program that included some serious investigation of the airbox and intake tract, Doug Henry's supermoto tuners left the screen in place all last season on his YZ450 . When he won he Irwindale race I don't recall Doug saying, "I could have won by a bigger margin if someone would have just removed that damn backfire screen". :cry: After lots of hours of flow bench testing on the YZF airboxes dating back to March of 1998 every YZF we've built has included the recommendation to leave the screen in place if the bike is using the OEM airbox. There are plenty of other pro and soon to be pro riders out there running with screens in place.

So what is the point of removing it .....



I can only conclude that it somehow empowers a handful of well meaning but misinformed people. Either that or someone out there has an powerful aversion to wire mesh and will do anthing to rid the planet of it's scourge. :cry:

  • YZ250F_Rider

Posted October 17, 2004 - 09:16 AM

#13

Are you saying no one at pro level removes air screens, or that he didnt. since he didnt and it agrees with your views all others are misinformed?

Word has it air screens are harder to find on the tracks that hens teeth. Well except one apparently. :cry:

  • Rich_Rohrich

Posted October 17, 2004 - 11:09 AM

#14

Are you saying no one at pro level removes air screens,


Nope, I'm sure there are lots of bikes running without them. In light of the data I've gathered on my own and seen from sources I trust, their justification for doing it that way is of little interest to me.

All I'm really saying is that I found it interesting that when subject to proper analysis by a development team lead by the guy who is now the technical director of the Renault F1 team they found the screen posed no restriction that warranted it's removal. I found similar results in the last 6 years of testing both on the flow bench and on the track. Ron Hamp from RHC found similar results in his testing if memory serves correctly. Just sharing some feedback from a variety of sources. If you feel it isn't valid feel free to ignore it. It's still a free country, do what makes you sleep well at night.

  • Satch0922

Posted October 17, 2004 - 11:28 AM

#15

My bike does not have one and I still got pimped by and 85 rider at Splendora last weekend! LOL :cry:

  • Rich_Rohrich

Posted October 17, 2004 - 11:33 AM

#16

My bike does not have one and I still got pimped by and 85 rider at Splendora last weekend! LOL :cry:


Maybe if you took that pesky chain guard off you'd smoke the little bugger. :cry:

  • Joe_Jet

Posted October 17, 2004 - 11:43 AM

#17

It was easy to remove on the Hondas. When I pulled it off my 03 CRF 450, I don't remember a huge gain. But, when I pulled it off my 04 CRF250 it made a noticeable difference down low. Almost as much as an exhaust system!

  • YZ250F_Rider

Posted October 17, 2004 - 11:44 AM

#18

Everyone I have seen try this says it requires a larger main jet afterwards, and that the bike is faster afterwards as well. I've verified it on 2 yz250f's and now on the 05 450.

I'm am curious with all of your in depth analysis if you bothered to cut the rear wall of the airbox down at the same time as removing the air screen. And included running a low back pressure silencer.

  • grayracer513

Posted October 17, 2004 - 06:54 PM

#19

OK, now I'm curious.

If we agree that the bottom of the seat, the two subframe tubes, and the rear wall of the airbox form a roughly rectangular opening through which air can enter the air box ( and momentarily forgetting that it isn't the only way for air to get in there), and that this rectangle is roughly 4 times the size of the carburetor bore, how exactly does that help?

Let me just suggest that if you were to connect the assembled airbox, fender, subframe and seat to a flow bench you would find that it will flow more air than a 450 can use. At least, that's what it looks like to me.

  • motobark

Posted October 17, 2004 - 07:51 PM

#20

Everyone I have seen try this says it requires a larger main jet afterwards, and that the bike is faster afterwards as well. I've verified it on 2 yz250f's and now on the 05 450.




But, when I pulled it off my 04 CRF250 it made a noticeable difference down low. Almost as much as an exhaust system!




Give me a break! If you guys can tell a noticeable difference from taking out a backfire screen, why does anyone bother using a dyno, why don't they just have guys like you ride the bikes. I've got $100 that says I can switch air cleaners all day long in your bikes and you won't be able to tell me if the screen is in or not.

I have two words of advice, first is listen to Rich, he knows how to VERIFY A THEORY WITH FACTUAL, REPEATABLE, HARD EVIDENCE.

Second is, keep in mind the power of suggestion. Evaluating any change in your bike is very difficult when you have a preconceived idea of what to expect. You expected it to be faster, so naturally it felt stronger. Try not making a change and evaluate your bikes power from one ride to the next. Or better yet, have your buddy make the changes on your bike and tell him to NOT tell you what he did.

I've worked on cars for over 35 years and I've seen the power of suggestion over and over. Here's a good example... All I have to do is drive a car in, open the hood, wave a few tools over the motor, close the hood and back it out. Then I tell the customer, "I made some adjustments, it should run much better now". 8 out of 10 car owners would swear "it runs SO much better!"
(No, I don't actually do that to people.)

I do have one more piece of advice, IT IS the rider, not the bike. Stop blaming the bike. It amazes me how much time and money is spent trying to get that extra 1/32 of a hp when skill makes such a huge difference. The average "C" rider is using about 1/4 of the potential of a YZ450, if he makes the bike faster it just means he's down to 1/5th of the potential. Shouldn't the goal be to get the potential of the bike a little closer to the potential of the rider? I learned to ride on relatively underpowered bikes, and guess what, it made me a better rider because I HAD to learn things like momentum, flow and not scrubbing off speed in turns.

John





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