Backfire Air Filter & Screen - Part 2
#1
01-28-2007 | 11:54 AM
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Senior Member
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Joined: Jul 2006
Posts: 966
From: Ottawa, Ontario
Backfire Air Filter & Screen - Part 2
In Part 1, we confirmed that the Twin Air Backfire Filter for all Yamaha YZ 4 strokes (Twin Air Part No: 152313) will fit inthe KLX250S.
Here in Part 2, we will remove the KLX250S backfire screen.
Here's a picture of the backfire sreen. You can get to it by removing the seat, opening the airbox, and removing the air filter:
I lucked out and had the right tools that allowed me to remove the screen without having to remove and dismantle the airbox itself. Regardless if you can remove the screen this way, or not, I do not recommend cutting the screen out while it is still inside the airbox!!! You'll see why soon enough. The tool on the left is a Motion Pro Folding Trail T-Handle Set with a 1/4" drive. It does not come with theuniversal joint shown in the picture, but the key is the universal joint. The needle nose vise-grips on the right are clamped on to an 8mm socket.
The backfire screen is held on with 4 nuts. The studs are permanently embedded into the plastic airbox. Here I'm using the Motion Pro T-hanlde to remove one of the nuts. This one is easy and so is the lower one on the same side. The top nut on the other side is the tricky one. This is where the universal joint is a must ... a small 1/4" drive ratchet may also work instead of the T-handle.
The last nut at the bottom is pretty hard to find. I put the socket on it so you can see where it is in the picture below. The needle nose vise-grips are used to loosen this one. (For anyone who's drilled a 3/8" hole in the airbox for the crankcase breather, the technique is the same: Clamp-Rotate-Release-Repeat).
Once all 4 nuts are removed, you have to wiggle the backfire screen around a bit, and its a tight squeeze, but it does come out the top (just barely):
Take note here that the screen is not symetrical, and it only goes on one way:
Now, the whole point of this exercise ... getting rid of the screen. Just poke your wire cutters through and start cutting:
One down, two to go. Notice the little collection of bits and pieces ... not all of them fell straight down!
Threemore items to add to my OEM parts box:
A quick sanity check to see how things are going: Yep, nothing but blue skys! No restrictions here!!!
The screen itself is molded into the plastic, which is why it needs to be cut out. The edges aren't clean and there are small bits of wire left that can tear the foam air filter, so a bit of filing and sanding is needed to clean it up. Here is the finished product:
And the other side:
The operation is a success!
On to Part 3 - Tailoring the Twin Air Filter for the KLX250!
Here in Part 2, we will remove the KLX250S backfire screen.
Here's a picture of the backfire sreen. You can get to it by removing the seat, opening the airbox, and removing the air filter:
I lucked out and had the right tools that allowed me to remove the screen without having to remove and dismantle the airbox itself. Regardless if you can remove the screen this way, or not, I do not recommend cutting the screen out while it is still inside the airbox!!! You'll see why soon enough. The tool on the left is a Motion Pro Folding Trail T-Handle Set with a 1/4" drive. It does not come with theuniversal joint shown in the picture, but the key is the universal joint. The needle nose vise-grips on the right are clamped on to an 8mm socket.
The backfire screen is held on with 4 nuts. The studs are permanently embedded into the plastic airbox. Here I'm using the Motion Pro T-hanlde to remove one of the nuts. This one is easy and so is the lower one on the same side. The top nut on the other side is the tricky one. This is where the universal joint is a must ... a small 1/4" drive ratchet may also work instead of the T-handle.
The last nut at the bottom is pretty hard to find. I put the socket on it so you can see where it is in the picture below. The needle nose vise-grips are used to loosen this one. (For anyone who's drilled a 3/8" hole in the airbox for the crankcase breather, the technique is the same: Clamp-Rotate-Release-Repeat).
Once all 4 nuts are removed, you have to wiggle the backfire screen around a bit, and its a tight squeeze, but it does come out the top (just barely):
Take note here that the screen is not symetrical, and it only goes on one way:
Now, the whole point of this exercise ... getting rid of the screen. Just poke your wire cutters through and start cutting:
One down, two to go. Notice the little collection of bits and pieces ... not all of them fell straight down!
Threemore items to add to my OEM parts box:
A quick sanity check to see how things are going: Yep, nothing but blue skys! No restrictions here!!!
The screen itself is molded into the plastic, which is why it needs to be cut out. The edges aren't clean and there are small bits of wire left that can tear the foam air filter, so a bit of filing and sanding is needed to clean it up. Here is the finished product:
And the other side:
The operation is a success!
On to Part 3 - Tailoring the Twin Air Filter for the KLX250!
#4
01-28-2007 | 09:02 PM
Member
1st Gear Member
Joined: Dec 2006
Posts: 73
From: Harriet, Ar.
RE: Backfire Air Filter & Screen - Part 2
I found that my 1/4 drive socket set would not fit in the lower recess. Never mind trying to put a U-joint in between. I ended up using a cut off wheel and shortened a socket, then cut off the end of a Allen Wrench and filed it until the socket would fit on the end, to get something short enough to do the job. The vise grips might have been the better option. But here is my first attempt at posting a picture.
#6
06-02-2010 | 09:14 AM
Senior Member
1st Gear Member
Joined: Apr 2010
Posts: 471
just a simple question.. removing this screen does not seem in my mind to provide any significant air flow increase. I am willing to bet that there is no difference between having this screen on and not having it.. same holds true for spark arrestors on slip on exhaust.. anyone agree here?
#7
06-02-2010 | 09:55 AM
just a simple question.. removing this screen does not seem in my mind to provide any significant air flow increase. I am willing to bet that there is no difference between having this screen on and not having it.. same holds true for spark arrestors on slip on exhaust.. anyone agree here?
No to both.
No spark arrestor in my 2 Brothers M7 and no backfire screen in the airbox.
It did clean up my jetting off idle, so there is an improvement IMHO.
these mods are free too.
#9
06-02-2010 | 10:44 AM
Senior Member
1st Gear Member
Joined: Apr 2006
Posts: 1,433
From: Olympia WA
no SIGNIFICANT air flow increase. The only thing that I could measure the difference with would be the SOTP Dyno Meter found here----> http://kalecoauto.com/index.php?main...products_id=41
