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The guitar, not the fish!
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Discussion Starter #1 (Edited)
Seems like every week I get at least one (usually more) PM's asking me about how I did the decapitation mod to my factory airbox...While I have no problems with helping my fellow Xr's, I keep repeating the same info over and over and over and, well you get the idea....So I decided to just take the time to post up a how-to that anybody can reference...By doing this you gain two positives...First is the additional airflow over totally stock..The factory setup is pretty restrictive and chopping the top off completely opens up the top of the airbox, allowing it to flow ALOT more air...Second if it's done the way I did, you can from this point forward, remove the airbox with the gas tank still in place on the bike....Makes getting at the carb a much quicker process....

First remove the airbox cover and filter, with the gas tank and everything else still in place...Then using a white grease pencil, I traced along the bottom edge of the gas tank onto the black plastic airbox...Then remove the gas tank..Here's a how-to on gas tank removal if you need it...http://www.vtxcafe.com/showthread.php?t=33679 Then remove the airbox from the bike..There's three screws at the carb, a bolt near the bottom, and one near the top...Also there's the crankcase vent tube in the back of the cover, and the tube for the PAIR valve system if you haven't already removed that from the bike...Once you have it off the bike, the fun parts starts...I used a cutoff wheel in my die grinder, but I know that not everybody has an air compressor at their disposal..A cutoff wheel in a Dremel will also work, and as well as a hacksaw...I chose the easiest and quickest way I had....Using the grease pencil again, continue the line you already drew around the sides and back of the airbox....Now when you start cutting, cut ABOVE the line you just drew, especially on the back....If you cut too low on the backside, you'll end up allowing unfiltered air into the carb, and you don't want that happening...So you need to stay above the flat area back there...Once it is cut, it'll look just like this....



See that flat area at the top that I left?...Don't cut into that, or you'll be letting unfiltered air into the carb...Might take2-3 times to get it right...I cut it high all the way around, then went a little at a time until I could get it back on the bike with the gas tank in place back on the frame...I left it high on the backside, and when I remove the remaining mount locations (one gets cut off), I tilt the bottom out towards me so the backside will clear the tank bottom...Here's what it looks like with the tank off the bike...



Big difference in the open area between this and the two small openings that were formerly the intake openings...You can also see how the filter sits in there, and why it's important to leave that flat area intact...Now all that's left is to put it back together...The crankcase vent tube on the backside can be a pain to re-attach, but it'll go back on there...Here's what it looks like all re-assembled on my bike with my waterjet-cut airbox cover by Lazerdude...Can't even tell it's been cut with it all back together..



Now for a couple more items that need to be covered...Doing this allows alot more air to enter the carb and engine, so carb work is needed to keep the air/fuel ratio correct...Lots of other guys here have done this same mod, and I'm 99% sure that everybody here has followed Scar's carb tuning sticky to dial in their setup..We're all using 2 shims on the stock needle, and set the A/F screw to 2-1/2 turns out from lightly seated...With my particular setup (opened airbox cover + decap, I have the A/F set at 2-5/8, and could maybe use another 1/8 turn which I'm gonna try this year....

Also I recommend getting a K&N filter...The stock one is a paper filter, and with the top chopped off the airbox, there's a decent chance of water getting in there if you get caught in the rain...Water will destroy the stock filter, but a K&N will be fine for the life of the bike...

Best thing about this mod is nobody can tell it's not 100% stock...But it'll flat haul ass when the carb is dialed in to the increased airflow...Stealth mode at it's best!!..LOL!!...:mosh:
 

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Thanks bass. Great writeup. I have been waiting to do this and the scar mod to the bike. You should get a moderator to put this with the other sticky threads at the top of the 1300 forum. Thanks again, this is a great service to us that are looking to do it.
 

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Really appreciate the write-up Bassdude - I have been debating on doing this mod next on my bike. I really like the idea of doing low and no-cost mods to my bike. That keeps me and the wife happy! Here is my dilemma - Right now my bike runs good with the stock set-up. Only mods done to the drivetrain are PAIR valve removal to clean things up and deep Clayton mod. (Oh yeah - and the seat pin mod - that alone is worth at least 10 HP -right? ;)) Starts fine with no choke, just a twist of the throttle before hitting the button, and I have no complaints on driveability. SO... how much tinkering is required to get it right after the mod and how much improvement are we talking about? Also - I don't see how water gets in if you don't do the "waterjet-cut airbox cover by Lazerdude" - what am I missing? And, lastly, how does it sound sucking all that air and how noticeable is the sound? Hope that's not too many questions - just don't want to do it and then wish I hadn't. Had a Trans Am a couple of years ago that I did a lot of mods to and the more I did to it the less I drove it. Don't want to make that mistake again...
 

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The guitar, not the fish!
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Discussion Starter #7
Starts fine with no choke, just a twist of the throttle before hitting the button, and I have no complaints on driveability. SO... how much tinkering is required to get it right after the mod and how much improvement are we talking about? Also - I don't see how water gets in if you don't do the "waterjet-cut airbox cover by Lazerdude" - what am I missing? And, lastly, how does it sound sucking all that air and how noticeable is the sound? Hope that's not too many questions - just don't want to do it and then wish I hadn't.....
Like I said, I was in the middle of tuning the carb per Scar's write-up when I decided to decap the airbox...Lot's of other guys running the decap mod with totally stock cover, with 2 shims, and about 2-1/2 out on the A/F screw...If I remember eight, I had it all dialed in by the end of the day, and I've been running it that way for almost two years now, and haven't had to touch the carb once...Very reliable...

As far as water getting in, if you ride in the rain, water could possibly run down the backbone of the frame and get in that way...Wouldn't be alot, but it won't take much to destroy the stock paper filter...

As far as intake noise, there was a big difference when I added the waterjet-cut cover...Don't remember if it got louder with the decap or not..Maybe someone that has done the decap and still has the stock cover can offer their experience on this...
 

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Hey Bass, sorry. I must have been the cause of this post. Bassdude sent it to me once and till I was ready I lost it. Then I asked the second time. Bassdude, the good news is, bike in downstairs and mods will be tackled as soon as we get home. Thanks for your help man!!
 

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The guitar, not the fish!
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Discussion Starter #10
Hey Bass, sorry. I must have been the cause of this post. Bassdude sent it to me once and till I was ready I lost it. Then I asked the second time. Bassdude, the good news is, bike in downstairs and mods will be tackled as soon as we get home. Thanks for your help man!!
Don't be sorry, no need...I've been getting PM's about this for the past several weeks now, about 2-3 a week...So I decided to just do it this way instead of re-typing the same info over and over...Been hanging oot at the "other" site also and getting the same questions over thetre, just not as frequent...So now when that happens, I'll post the link to this site instead....:stirpot: :D
 

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PEOPLE CALL ME GERSTY
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I have Gonzo coming over to help me tackle this with the scar, I bought new champ plugs for it, got the washers, Glens perm, a/f screw and got a k&n filter, I am gonna be running the stock airbox cover so i will be able to put my two cents in about the air sucking sound if its louder or not, As everyone else has already stated Thanks for the great writeup Bass.
 

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Hay nice job.

I got to get a new camera, I can't get good pictures in the garage. So thanks for your pictures and write up.



Don't be sorry, no need...I've been getting PM's about this for the past several weeks now, about 2-3 a week...So I decided to just do it this way instead of re-typing the same info over and over...Been hanging oot at the "other" site also and getting the same questions over thetre, just not as frequent...So now when that happens, I'll post the link to this site instead....:stirpot: :D
Having been over at the other site, I got to say the people that are on here are a lot more plesent. On the other site people would be telling you your nuts for doing this, or you should have done it a drifferent way. LOL:spank:
 

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Hey Bass, if I may sir, don't want to highjack but Scar mod needs to go with your decap mod.
This looks to be a good video of Scar Mod done right in front of your eyes. It starts with the seat, tank and airbox off. Ready to go right into the carb. Looks like this will put many of us at ease. Looks VERY easy. Take a look but Beware you'll be wrenchin' soon.

http://www.goheengarage.com/tutorials.html

Bass maybe you can edit and add this to your O. Post at top.
Whatever you choose Bass.
Later All,
Smoke
 

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The guitar, not the fish!
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Discussion Starter #15
.Bass maybe you can edit and add this to your O.
Huh????...:confused:
Having been over at the other site, I got to say the people that are on here are a lot more plesent. On the other site people would be telling you your nuts for doing this, or you should have done it a drifferent way. LOL:spank:
Actually, a year or so ago we had a new member that was fresh out of "bike mechanic" school that was severely bashing all of us that drilled pipes and modded airboxes from factory...Said that the factory engineers knew what was the best and we should leave all our bikes totally stock...Yeah, like that's gonna happen!!....LOL!!...He didn't stick around long...Every once in awhile we get somebody like that, and they don't stay long once they see what we're really all about....Prolly why if Honda themselves actually visit this site, they don't make themselves known...
 

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If man makes it, Man can and will modify it !:bleh: Besides how do peeps like that expect to make a bike your own if ya dont Mod it ? Great tutorial on the scar mod, I will be doing this mod in the next day or so.
 

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Great write up Bill.
I did this mod right after he originally posted it and love it. I'm running the stock cover, and pipes are Kiwi modded, and I am using 2 shims with the A/F screw at 2 turns out. I don't really remember hearing it suck air any louder after doing it than it did before, but i don't have a lazer cut cover on mine.
 

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FDC !! The Real Truth...
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+100 on the write up Bass..... I have the exact same setup across the board... I don't hear much of a sucking sound or overly loud air sounds as a result of the decap to the air box. A bit from the front right side due to the lazercut cover but that's about it.... My Street Sweepers pretty much rule the sound overall.... I will say this... Having just this mod "decap the airbox" is worth it's weight for sure.... but coupled with any open air cover, the SCAR mod, the PAIR valve mod and dialed in around the 2 to 2 1/2 turns on the A/F? Well now those will give you such a kick in the pants power boost that you will never stop cheezin.....
 

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Thanks again for the write up...I did this a couple weeks ago and now the weather is warmin up a bit I got to go out and test it out completly....one of the best things I could've done with the bike! And it's free!:mosh:
 

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Great write up

Hopefully I am sort of on topic here with this question.

I see lots of discussion about the pair valve removal, the air box decapitation, scar mod and the opening the air breather covers. The general consensus is that this does give the bike more power and better throttle performance. I understand all that and can see the benefits. What I am not seeing in these threads is any data on how or if these modifications effect the gas mileage of the bike and to what degree.

I figure with the way some of you guys keep records, there most be some empirical data out there from before the mods and after the mods for a comparison of the power and performance increase to the miles per gallon ratio. I most admit to being as mechanically inclined as a brick, so in my mind I am thinking if power and performance goes up, gas mileage going down is the most likely direction. However since I don't know the answer I figured I would throw the question out to the group.
 
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