Can a side panel vent mod correct fuel mixture?

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Can a side panel vent mod correct fuel mixture?

Post  BlindDude on Mon May 29, 2017 7:59 pm

I will try to make this short.
2002 xr650r, Just purchase yesterday. The elevation I purchased it at is 4200'. The seller informed me that he had it jetted for 3500'. When I asked what numbers the jets were, he didnt recall..?
I live at 6000' and the mountains around me go up to 9000'.
At 4200' the bike ran STRONG, no hesitations or hiccups in throttle range..
Here at 6000' it starts to "blurp" at around 1/4rpms then clears up and then "blurps" again at around 3/4rpms. <-if that makes any sense?
I am wondering if I were to vent the side panel, this may let in more air and maybe let me avoid jetting?
I took apart my carb on my '03 xr650r years ago and remember that I never wanted to do that again.
So if I start slow, a few holes at a time, then check how it runs, do you think I could get the correct mix this way?
Thanks for any info on this. I am sorry I didnt search much, I did a little, but I just dont have time to look through a bunch of "kinda" relevant threads. Being I am taking care of a handicapped kid 24/7..

Edit: A few hours later.. I have drilled 5, 5/16" holes in a triangle shape above the biggest part of the k&n filter. The "blurps" I spoke of seemed to happen a little bit LESS.. So, I drilled again, maybe 10 holes total and it ran even BETTER, So now I put 15, 5/16" holes in it and she seems to run really good through the throttle.

Only thing I can notice now is while cruising at a set speed, it will hiccup and blurp, just slightly. But runs good while revving from idle through the gears to redline. I plan on drilling more holes, probably as many as I can without impairing the integrity of the panel.


Last edited by BlindDude on Mon May 29, 2017 11:03 pm; edited 1 time in total (Reason for editing : More info learned)
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Re: Can a side panel vent mod correct fuel mixture?

Post  Mauser on Tue May 30, 2017 8:49 am

Sounds like you answered your own question, I wouldn't have drilled to start with but tried the bike without the air filter element present for a few miles to see if airflow was the culprit....but your sorted. Not sure about the constant speed problem maybe you have an air leak somewhere ?

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Re: Can a side panel vent mod correct fuel mixture?

Post  BlindDude on Tue May 30, 2017 9:02 am

Mauser wrote:Sounds like you answered your own question, I wouldn't have drilled to start with but tried the bike without the air filter element present for a few miles to see if airflow was the culprit....but your sorted. Not sure about the constant speed problem maybe you have an air leak somewhere ?

Thank you for the reply.
I just cleaned and oiled the K&N and it never even crossed my mind to take the filter out, or even try it without the side cover too.. I will do that tomorrow to see if I need to open it up even more. I just drilled above the big squarish part of the filter.

Having a leak somewhere is a joke right? You making fun of all the holes I made? lol
Or is that really a problem? Leak from where? Fuel line maybe?
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Re: Can a side panel vent mod correct fuel mixture?

Post  BuRP on Tue May 30, 2017 2:38 pm

I didn't read because I saw "K&N" filter mentioned.
Wrong filter dude, chuck it and get yourself a foam filter, UNI or TwinAir - or the OEM filter, but DO get rid of the K&N!
Reason is they let fine dust trough, and this is exactly where you'll ride it......
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Re: Can a side panel vent mod correct fuel mixture?

Post  BlindDude on Tue May 30, 2017 5:24 pm

BuRP wrote:I didn't read because I saw "K&N" filter mentioned.
Wrong filter dude, chuck it and get yourself a foam filter, UNI or TwinAir - or the OEM filter, but DO get rid of the K&N!
Reason is they let fine dust trough, and this is exactly where you'll ride it......

Holy crap, are you serious? Ok... I never heard of this. Does k&n have some sort of recall? That was the most expensive filter out there.
I am not questioning you but do you have a link or something to the K&N issue? And that would mean that most all k&n filters suck? Cuz they are all mostly built the same right?
Thank you
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Re: Can a side panel vent mod correct fuel mixture?

Post  BuRP on Wed May 31, 2017 3:01 pm

Yes, crap indeed, it is a cotton-gauze filter.
Look through it held against a lamp/sun, and I bet you'll also see light through it - tiiiiny pinholes however millions of them.
These let fines through - no problem (well...) for a trackbike so I actually have one in my 600: the bike gets plenty of air but the stones etc are kept out.... notalot of fines on asphalt if you know what I mean.
But offroad, geezz, a no brainer: oiled foam!

Recall ? ? ? ?
You must be a Yankee lol!!!!!
Hell, try by all means but they'll deny it in any case, and here's why:
A cotton gauze filter when clean&oiled lets more air through than any other type of filter!
But, it thus (yes, THUS) also will allow quite a bit of fines through - it filters less because it passes more air, capiche?
However, during use some dirt captured in the oil settles on the gauze - and it thus does 2 things 1) it lets less air through, and 2) it starts to filter better!
It goes without saying that those having these filters in an offroad application do best NOT to clean their filter too often, in fact best to leave it dirty-ish.

In stark contradiction is how a (oiled) foam filter works.
When these get filthy, and I am talking about literally cup-loads full of dirt on the outside (not kidding, ask any of the motocrossers here) then they still flow an astonishing amount of air i.e do not really affect the performance of the engine - and correct, they still filter well.

You choose bru, it's your bike! Wink
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Re: Can a side panel vent mod correct fuel mixture?

Post  BuRP on Wed May 31, 2017 3:08 pm

To complete this saga, the best filtering filter is a paper element!
It is cheap, it filters best and can be designed to flow plenty/enough.
But.... if they get wet they block (or may puncture!), and if they get dirty they block hence must be replaced.
Our consumerism-society has long time since adapted to 'replacing' and this keeps an entire industry going, so no surprise that your car has a paper element, and plenty of bikes do too.
For offroad bikes (and cars too I think) an oiled foam filter proves best, for it can handle what looks like abuse whilst still flowing & filtering well.

On the opposite side sits 'maximum performance' i.e NO filter - F1 anyone?
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Re: Can a side panel vent mod correct fuel mixture?

Post  BlindDude on Wed May 31, 2017 6:23 pm

Thank you Burp.
I sure hope not too much damage has occurred.
I will order a uni. I hope it lets good air through cuz I got the side panel drilled to where I want it for the k&n.. But I only drilled maybe less than half of the total area drillable.
I wonder if uni and twinair are still in production? Or are the filters I find old stock? I ask because I havent had good luck with foam getting old sitting on a shelf.. Turns to shit after a while.

ME!


Last edited by BlindDude on Wed May 31, 2017 6:25 pm; edited 1 time in total (Reason for editing : Too many I's and wanted a little ME in there. lol)
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Re: Can a side panel vent mod correct fuel mixture?

Post  BuRP on Thu Jun 01, 2017 9:48 am

As far as I know both UNI and TwinAir are going strong as ever.
Yip, old foam can get dry & crusty, time for replacement then - actually a little earlier lol.
But, I keep my spares oiled & in a ziplock bag, laid flat of course, not rolled up or squeezed in any manner - out of any sunlight, in the dark is best.... they last.

On UNI, they have, or perhaps had, 2 types: one consisting of a dual (atually triple with hte inner thin gasket layer) foam layer without any metal nits, and one with an integrated metal screen. The latter allegedly does not need an additional (anti-backfire) screen which this bike has, but I don't like this - but it will do if you can't get the foam-only type.
The std screen is best, however also a bit restrictive as it is quite dense. XRsOnly sell a more open screen which I have, and I like it, prefer it even. Some have complained about fitment but mine fits well.
The function of this screen (whether loose or incorporated into the NUNI-filter) is to prevent the filter burning (risking your bike!) when the engine backfires - hence a no-brainer, you must have one!

On the side panel itself, 'opening' it has some advantages - but also a drawback!
It lets more air in hence one can jet for a bit more performance.... however, the std (with the plugs removed of course) intake area is sufficient for good performance. Oh, yes, mine is opened also.
The drawback is that your wading-depth is reduced with an open panel, just keep this in mind.

An added advantage of a open sidepanel is that, during a trip spanning a really large altitude differential, one may be able to 'tape off' the sidepanel (i.e closing it) to compensate for jetting problems, this rather than carrying jets and fiddling inside the carb. A closed-off panel at sealevel may be opened at high altitude to keep things 'as best as possible', this all with the same jets in the carb.
And yes, some tape may also come in handy during deep watercrossings.
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