air filter heresy

[DogBunny]

I was reminded yesterday that it is heresy on this forum to recommend anything other than UNI air filters. In particular, Forum Doctrine dictates that "pleated" or "K&N style" filters are evil and are to be avoided at risk of loosing your soul.

For BS38: https://yamahaxs650.com/product/52mm-xs-performance-pod-filter/
and for BS34: https://yamahaxs650.com/product/54mm-xs-performance-pod-filter/
Well, the XS Performance pleated K&N clone filters work just fine, at least they do for me. I've put plenty on BS38 carbs, and a few on BS34s. I've used plenty of UNIs too. I see zero difference in performance. I do see plenty of difference in cost and durability. The XS Performance filters have been on sale at yamahaxs650.com for ever, at half the cost of UNIs. And the UNIs eventually fall apart, at least they do for me. They simply are not robust, which the XS Performance filters are. They are very durable, and for me, they last forever.
I use genuine K&N spray can filter oil on them, which sprays out red/pink. Yeah, It's a lot more expensive than using a brushed-on 50/50 oil and kerosene mix on your UNIs, but it's a whole lot faster and more convenient. You can afford it with all the money you save on the Performance filters.
One more thing. UNIs look just fine, but the Performance filters are way sharper, in my opinion.

 

[atom4488]

A provocative post no doubt... I have no dog in the fight, so I'll just sit back to see if any fur flies !

 

[willis]

I run stock airboxes with stock filters. I did pick up a set of K&N slide in filters for the stock airbox on my 77 project, but I've never ran them yet. It is my understanding that the pleated pod style filters can cover a port in the bell mouth of the carb which causes issues. I don't recall the conversation of the pleats causing turbulence. I'd be interested to hear those thoughts on that though.

 

[DogBunny]

Many of the round pleated filters, like this one, will block ports. I don't have any experience with K&Ns.
I guarantee that the XS Performance oval pleated pods don't block anything, not even a little bit.

On a bike that gets ridden a lot, I don't think I have ever had UNIs last more than 5 years, if that.

 

[650Skull]

I was reminded yesterday that it is heresy on this forum to recommend anything other than UNI air filters. In particular, Forum Doctrine dictates that "pleated" or "K&N style" filters are evil and are to be avoided at risk of loosing your soul.
View attachment 326533
For BS38: https://yamahaxs650.com/product/52mm-xs-performance-pod-filter/
and for BS34: https://yamahaxs650.com/product/54mm-xs-performance-pod-filter/
Well, the XS Performance pleated K&N clone filters work just fine, at least they do for me. I've put plenty on BS38 carbs, and a few on BS34s. I've used plenty of UNIs too. I see zero difference in performance. I do see plenty of difference in cost and durability. The XS Performance filters have been on sale at yamahaxs650.com for ever, at half the cost of UNIs. And the UNIs eventually fall apart, at least they do for me. They simply are not robust, which the XS Performance filters are. They are very durable, and for me, they last forever.
I use genuine K&N spray can filter oil on them, which sprays out red/pink. Yeah, It's a lot more expensive than using a brushed-on 50/50 oil and kerosene mix on your UNIs, but it's a whole lot faster and more convenient. You can afford it with all the money you save on the Performance filters.
One more thing. UNIs look just fine, but the Performance filters are way sharper, in my opinion.

For some reason your links aren't loading. Keep getting "web page not available"

Nice to have feedback on these. Does seem to b common knowledge . Honestly there has been a few bits of advice given that people have followed and reposted, that has changed due to real time experience .

Did you find a difference in jetting between the UNI's and the pleated filters. Curious as to the amount of air flow difference between the 2

 

[DogBunny]

The links work for me. You could try going to yamahaxs650.com and then going through the categories.

I did not need to change jetting.

yamahaxs650 is pretty low on stock of these filters. I just ordered several of the BS38 size and one pair of the BS34 size. That leaves about 10 of the BS38s and 15 of the BS34s as I write. After that, you'll have to buy from Mike's at 3X the cost.
yamahaxs650's "team" is on a purchasing trip as we speak, presumably to Taiwan, with a return date of the 28th.

 

[650Skull]

For some reason the site will not open. Through your links, me typing yamahaxs650.com or using a link to the site through a search engine. No matter I'm not interested in buying off them and with the exchange rate right now it adds a third into any price + a 1/3rd on the postage.

Just bought a $20.00 part, (small part, postage envelope), off Gary, +$21.00 postage, $41US = $65 Australian. That was through pirate ship.

 

[5twins]

I started out with genuine K&N pods on my 650 when I first got it going (2005). The airbox was trashed so I went directly to the pods. It ran OK but I couldn't get the carbs tuned perfectly. I felt that the bike needed/wanted another size up on the mains but it wouldn't run through the upper midrange under heavy throttle without breaking up, and that was with the needles already leaned a step. Well, I soldiered on that way with one up on the mains (when I really wanted/needed 2) for about 5 years. Then I read a post here on the forum by a well respected member (MrRiggs) about UNI pods and how well they worked, so I decided to give them a try. This cured all my issues. I was able to go up another size on the mains and there was no upper midrange break-up. So I came to the conclusion it had to be the K&N pods causing the break-up.

Normally, as you increase the main jet size, eventually you get to the point where the bleed-over into the upper midrange makes it too rich and you get break-up or stumbling under heavy or full throttle. So you lean the needles a step and that usually fixes the issue. Then you could continue to increase the main jet size but I've found that usually brings the break-up right back. So, I kind of use that break-up as an indication that I've reached pretty much the max on main jet size. The big issue with the K&Ns was this was happening before I actually reached the ideal main jet size. I was a size smaller than I needed to be but the K&Ns were indicating otherwise, that I had reached my max size.

A local 650 guy told me many years ago that pods didn't work well on the 650, that they caused a phenomenon called "slide flutter". This is just as the name indicates - instead of lifting smoothly, the slide rapidly bounces up and down, or "flutters". I think he may have been right pertaining to K&N pods and other K&N pleated style ones. Sustained slide lift happens late on these CV carbs, like around 4K RPMs, and when they try to start lifting and "flutter" instead, you get the break-up. And this happens right around 4K, right where my break-up issues were. The slides on CV carbs rely on a smooth flow of air to lift properly. I don't think the pleated pod design delivers that, I think it's disrupted and turbulent. K&N airbox replacements seem to work fine and that's probably because they're farther away from the carbs. The air flow smooths out by the time it reaches the carbs.

So, I've had the UNIs since about 2010 and they seem to be holding up fine. Maybe your hotter, dryer climate is what's wearing yours out in 5 years? Now, most of this break-up I've mentioned will only show up if you work the carbs hard, use big handfuls or full throttle. These CV carbs are rather forgiving and will mask over minor jetting glitches unless you work them hard. Obviously, you don't drive around like this all the time, but for testing the jetting it needs to be done. If you just putt around all the time, you may never notice these issues. Maybe that's why you say the bike runs fine, you haven't pushed it hard enough to uncover the jetting glitches.

Try this test. This is how I test main jet size and the midrange to main transition area (to see if the needles need leaning). In 2nd or 3rd gear, from around 3500 RPM, roll the throttle wide open and run up to about 5500 or 6K RPMs. Watch for any break-up, usually in the 4 to 5K range. If you get break-up and you've already leaned the needles, that would indicate the mains are too large and you need to step down a size. Unless you're running pleated type pods, then the main jet size may be fine and it's the pods causing the issue.

 

[DogBunny]

You are probably the number one advocate for UNIs on this forum, so your response is interesting.
I ride very aggressively, often gabbing big handfuls of throttle at all RPMs, and I never experience break-up. At least, that's how it seems to me -- the bike just works, so I don't pay a lot of attention to it.
I think you are much more discerning than me, and that you take steps to super fine tune your carbs. I'm more of an "it works good enough" person.
I think the biggest difference that might account for our differing experiences is our exhausts. I run free-flowing exhausts. You seen to run aftermarket exhausts that are more free flowing than stock, but not greatly so.

On the bug Killer I have stock headers, and straight pipes with home-made baffles.

On the Super RustBucket I have this, no baffles.

On a bike running 76-79 BS38s, with pods and free-flowing exhausts, I have a pretty simple jetting formula, gleaned from your Carb Manual: Up 4 or 5 on mains, up one (or very, very rarely 2) on pilots, and lean the needle one slot. Used this formula on countless bikes, and have "fixed" several friend's poorly running bikes with it. Again, I don't super fine-tune. If the bike runs good I'm happy, but maybe my bikes could be made to run even better, or have better fuel economy. But, honestly, my bikes run just fine. Maybe I'm not grabbing big enough handfuls to see break-up, or maybe I've just learned how much to grab.
As for your many-years-ago local 650 guy's flutter theory -- I am a bit skeptical. I've never used K&Ns, and you, I believe, have never used XS Performance pods. I wonder if there is any difference. What I would really like to do -- I have several BS38 XS Performance pods coming whenever yamahaxs650.com returns form Asia. Assuming that you currently have a BS38 bike, I'd like to send you a pair, and see if you discern any difference, leaving the jetting untouched.

 

[BluzPlayer]

Need to check to see if I have have a pleated filter and if so what type. I know I have Unis.
I can set them up on a stock head with a 38 and measure the air flow. Not sure any variance equates to the issues described. Perhaps it would depend on how vast the variance is if it exist. Again, it may be irrelevant to the discussion. There is also a chance I might be able to test for a difference in the Port's turbulence caused by the filters by sliding my boroscope though .40 lifted valve and looking out to the carb. Add some smoke and it might be possible to visualize the air and how it moves.
No guarantees, but I think it might be possible.
A little bit of work, but if there is opinion here that the data might be useful I'll gather the parts and give it a go. Obviously both filters would need to be prepped the same.
I also think that the test suggested by @DogBunny above would provide the ultimate feedback. I find this topic to be very interesting.

 

[gggGary]

For some reason the site will not open. Through your links, me typing yamahaxs650.com or using a link to the site through a search engine. No matter I'm not interested in buying off them and with the exchange rate right now it adds a third into any price + a 1/3rd on the postage.

Just bought a $20.00 part, (small part, postage envelope), off Gary, +$21.00 postage, $41US = $65 Australian. That was through pirate ship.

you should check your paypal account skull.

 

[gggGary]

Following and I'll add my later, but I've seen some studies, real use A-B testing that suggest air box volume is HP's friend.

 

[Jim]

Following and I'll add my later, but I've seen some studies, real use A-B testing that suggest air box volume is HP's friend.

Yamaha... as well as other manufacturers blow (wink wink) through millions in airbox design.... DB's as well as flow. As a general rule, their design will vastly out perform aftermarkets.... generally speaking...

 

[BluzPlayer]

Yamaha... as well as other manufacturers blow (wink wink) through millions in airbox design.... DB's as well as flow. As a general rule, their design will vastly out perform aftermarkets.... generally speaking...

That is certainly one assertion.
Perhaps on stock motors, it  may apply.
Clearly Yamaha and it's racing teams disagree when it comes to high performance as evidenced in the attached pic with King Kenny.
In fact they ran the dreaded PLEATED filters.

 

[Jim]

That is certainly one assertion.
Perhaps on stock motors, it  may apply.
Clearly Yamaha and it's racing teams disagree when it comes to high performance as evidenced in the attached pic with King Kenny.
In fact they ran the dreaded PLEATED filters.


View attachment 326775


View attachment 326774

View attachment 326776

You mean to tell me a stock air box weren't tuned to a motor making twice as much power? It's not "one size fits all?" Say it ain't so....

Yeah, it pretty much goes without saying that a setup tuned to a specific head, carb and exhaust design, won't exactly be optimal when you change the design.

 

[5twins]

Pleated type pod filters are fine on straight slide carbs, which I'm sure is on Kenny's race bike, they just don't work well on CV carbs. I've used K&Ns on every bike I ever owned, either pods or the airbox replacement, and they always worked fine. That's why I went with them initially on my 650. But, this was the first time I tried the pod version on a CV carb, and well, it didn't work right.

There were two versions of the later linked BS38s, the '76 -'77 set and the '78 -'79 set. The jetting is very different on the two sets, and in fact, the main jet sizes fall at the extreme ends of the size range used in the 38s. The '76 -'77 set had the smallest mains ever used, 122.5's, while the '78-'79 set had the largest, 135's .....

That small 122.5 main is fine on an all stock bike but is easily and quickly outpaced when you start modding. So yes, it is possible to increase the mains as much as 4 or 5 sizes on this carb set. On the couple sets I've fooled with, I got up to a 132.5, 4 sizes up. Of course I tried 135's, but they proved too big, giving me that upper midrange stumble during the full throttle test with the needles already leaned a step. On the '78 -'79 set though, one would be hard pressed to get more than a few sizes above stock on the mains. I was only able to go 2 sizes above stock, to 140's, and that was with the UNI pods. The K&N pods would only allow one size up.

However, at the moment I'm running '78 -'79 BS38 carb sets on both my 650s with 142.5 mains. I was only able to do this because I swapped in leaner 5Z1 needles from an XS400. These actually produced flat spots (a lean indicator) in the upper midrange, something I've never encountered before. Increasing the mains another size fixed that but required me to lean the needles another half step with a shim washer. Normally, I don't like to run the needles at their extremes (1st or 5th slot) and this is the leanest I've ever run any (technically at a 1.5 clip slot, if there was such a thing). But it works and the bikes perform well. They pull hard and well above 5K when on those large 142.5 mains, and the off-the-line performance is strong as well. This was my main reason for installing them, this better "take-off" lunge in the lower gears. While this is a leaner (fatter) needle through most of it's range, it tapers to a sharper point so is actually richer when lifted fully. Now, why does that affect take-off? Because even though sustained slide lift doesn't occur until higher up in the RPM range, when you whack the throttle open as you take off, the slides do jump open momentarily. The richer tip on these needles gives the bike a richer shot of fuel, hence the better take-off lunge. Here's the stock 5O2 needle compared to the 5Z1 .....

 

[GLJ]

Clearly Yamaha and it's racing teams disagree when it comes to high performance as evidenced in the attached pic with King Kenny.
In fact they ran the dreaded PLEATED filters.

The discussed problem is with pleated filters causing "slid flutter" when used on CV carbs.
Only way TM slides flutter is if the rider gets nervous.

 

[jetmechmarty]

When the XS11000 group was active one of the members recorded the operation of his XJ1100. BS34 carburetors. XJ1100 airbox is a total PITA. Any he put a camera behind the carburetors with no filters or airbox and rode the bike hard. Slide fluttering was clearly seen. Also, vapor coming back towards the camera. I don’t know what it means, but interesting nonetheless.

 

[BluzPlayer]

Yeah, it pretty much goes without saying that a setup tuned to a specific head, carb and exhaust design, won't exactly be optimal when you change the design.

Well that is obvious.
Thing is..
At the highest level, IF a tuned airbox outperformed those pleated pods, Yamaha, Shell, etc, would have tuned a box to race with instead of simply throwing some pods on the bike.
It's seems to be just as obvious to me that if there was even a smidgen of power to be gained from a tuned air box over pods, the teams would have been running them.
Yamaha wasted NO resources in the drive to increase the xs650 power. Most certainly considering they completely redesigned the head to gain every ounce of power, designing an airbox to match it would have been simple. They left nothing on the table in the pursuit of power for the xs650 in the chase for a championship.
They ran what gave them the greatest amount of power they could compete with.
Of course they used every bit of data they had from the "millions" spent on airbox design in the engines design.
Obviously they felt that the pleated pods provided that advantage over an airbox configuration or you would be looking at an airbox under the King's ass instead of those pleats.

 

[Jim]

Thing is..
At the highest level, IF a tuned airbox outperformed those pleated pods,

Well, I didn't go back and check, but I don't recall anyone claiming anything concerning a stock airbox "at the highest level." You're stating the obvious... and arguing against a claim that was never made, or at least certainly not made by me.

When you modify an engine to get more power, the stock airbox is not the way to go. I think we all agree to that.