Should I vent my airbox?? (XR650R)


4 replies to this topic
  • HawkGT

Posted May 02, 2006 - 02:37 PM

#1

Should I open up the side of my airbox??

stock carb (for now)
Moriwaki headers and silencer w/ spark arrestor
engine internally stock (maybe a cam soon?)

What are the pros and cons of venting the airbox (sidepanel)?
Are there quality kits available for venting the sidepanel or is it better to fab your own?

I like the idea of being able to tape up a vented box as a method for making quick jetting changes on the trail. My last longer dual-sport ride started at 1300ft and reached almost 8000ft. It would be nice to tape up down low and remove the tape up high to try and get around making trail side jetting changes.

What kind of jetting changes did you all find was necessary when venting the airbox. I ask not because I can't figure the jetting out on my own but because I'm wondering how much more air will flow. One main jet size? Two? Three?? If the extra flow only amounts to one size I'd be less likely to make the mod.


FYI: I live at 1300ft. I was running a 178 main but found it was too rich in my rising (now 90+ and climbing) afternoon temps. A 172 feels OK in the heat of the day and nice and crisp (maybe barely lean) in the cooler (~75 deg) nights/evenings. I'm still playing with it.

  • wickedsprint

Posted May 02, 2006 - 03:02 PM

#2

I just vented mine, seems to pull a bit better up top, to me it was not worth the effort. I have an edelbrock carb so I can't help you to much with jetting.

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  • qadsan

Posted May 02, 2006 - 03:44 PM

#3

It's a cheap easy to do mod that has both benefits and drawbacks. I've seen a true 'repeatable' mid range HP improvement on the dyno with just this mod and jetting, but I no longer have access to the dyno printouts or the dyno to do anymore freebies.

Some downsides are the intake noise will increase and wet weather and or water crossing might present a problem. None of those were much of an issue for me, especially since I have a spare side panel that I can change to if needed. If worse came to worse while riding in driving rain, I could simply duct tape it closed, but I'm generally not riding when its driving rain unless I have to. With the stock carb, you may notice a little less hit off the bottom, but playing with the fuel screw will get some of it back.

Doing the mod yourself is quite easy, but Barnums sells a very nice looking anodized aluminum kit if you want to go that route. The Barnums kit is riveted on and looks very nice. They sell the kit by itself and the complete side panel with the kit installed if you want to go that way, but the stock Honda side panel isn't cheap by itself. Doing this mod yourself is just a matter of sketching some triangular openings on the back side of your side panel and cutting them out. Make the triangles on each side of the support rib, but don't cut out your supports. I use a large drill bit to drill each of the corners so they're nice and round and then cut the straight sections with a jig saw. I cut everything just slightly smaller by ~1mm than what it should be and do the finish work with a rasp and follow that up with a file so everything is smooth and perfectly symmetrical. You can find stainless steel screen with ~30 mesh from various industrial hardware supply stores and you simply cut it to fit over the support rib and cover the triangles. A high quality silicone can be used to adhere the screen to the inside of the side panel. I like the silicone because it's easy to remove in the event that I need to remove it, but I haven't really had the need to remove it...yet.

You can be as creative as you want if you don't want to do the triangles like Team Honda. Some guys make patterns by drilling holes, some cut different shapes and Uni Filter sells a 1" round filtered vent that I've seen people use several of in place of doing the triangles. Here's a writeup I did on this several years ago if you want get some more info & pics on this.

http://www.4strokes....h/honda/airbox/

As far as jetting goes, buy another main jet or two in their larger respective sizes from where you're at right now and see which one pulls better on top. You my find the 172 is still a good choice or perhaps the 175 with the side panel cut out. You've already got a 178 :crazy:

  • Ramcc4x4

Posted May 02, 2006 - 06:31 PM

#4

After I opened my side panel I had a huge flat spot I couldn't get rid of until I went to a 70s pilot. After that, it ran great. Mine is similar to the Johnny Campbell bike and even riding in the rain hasn't proven to be a problem.

  • slomotobug

Posted May 02, 2006 - 09:07 PM

#5

Should I open up the side of my airbox??

stock carb (for now)
Moriwaki headers and silencer w/ spark arrestor
engine internally stock (maybe a cam soon?)

What are the pros and cons of venting the airbox (sidepanel)?
Are there quality kits available for venting the sidepanel or is it better to fab your own?

I like the idea of being able to tape up a vented box as a method for making quick jetting changes on the trail. My last longer dual-sport ride started at 1300ft and reached almost 8000ft. It would be nice to tape up down low and remove the tape up high to try and get around making trail side jetting changes.

What kind of jetting changes did you all find was necessary when venting the airbox. I ask not because I can't figure the jetting out on my own but because I'm wondering how much more air will flow. One main jet size? Two? Three?? If the extra flow only amounts to one size I'd be less likely to make the mod.


FYI: I live at 1300ft. I was running a 178 main but found it was too rich in my rising (now 90+ and climbing) afternoon temps. A 172 feels OK in the heat of the day and nice and crisp (maybe barely lean) in the cooler (~75 deg) nights/evenings. I'm still playing with it.


It is a simple but rewarding mod, found much better mid and top, w/out losing bottom. Where in AZ are you? I have the perfect screens for the job, maybe i could just mail you a couple, I get them free from work, I used 2 3"dia SS screens that have an aluminum ring around them that works great to rivet them in, here's a pic, my cut job was a little rough, but functional, and the notch at the rear was my first attemp to get more flow, before I knew better.
Posted Image
Around the valley I always ran a 68s pilot, 175 main in summer, 178 in winter, needle in the 4th pos, side panel vented, intake mod, air box mod, pipe mod (my own version), and it always ran perfect. The only time I ever went leaner was if I was going to the cynders and I needed to squeeze every ounce of power out of it, and then I ran a 170-172 depending on the temp up there, but that's 7500-9000ft. On long rides that changed elevation I ran the 175 main, little rich at 8000, but as long as I wasn't trying to pull 5th up a wall, it was fine. The most elevation change in one ride I think we did was Sycamore to Young, sounds about like your long ride, started at about 2k and at times was around 7500, with the 175, it was fine.
Shoot me a pm if you want a couple screens, I have a ton of them cluttering up my toolbox, they work great for a removable spark arrestor too :crazy:





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