air filter heresy

[BluzPlayer]

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.

Hey Marty.
My best guess without seeing anything is that he was capturing some of the "reversion" that occurs within the port which is normal once the valve closes and the pressure starts to reflect back up the port towards the carb.
At the highest levels the intake manifold length is tuned for these "waves" in order to move either the torque or power curves to the desired rpms.
Could be something else entirely.

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.

Hey 5twins.
I think this is the most likely answer.
I have not been able to find the precise info on the carbs used. You always supply straight forward and very solid information.
Your work with these carb sets is legend.
I am hoping you will accept the offer from @DogBunny to swap and test.
I know you can be counted on to give an honest evaluation. It has been a lingering question within these pages for some time. Most information to be found is anecdotal, and such a test could possibly provide something more concrete.

 

[650Skull]

Not obvious, just an observation. All the chatter regarding uneven air flow and slide flutter has revolved around those cheep small pods that often block or parshley block the vacuum port. Some people, have said the ones they bought don't, some have cut the offending lip off. The small tapered pods have a small surface area.

The k&N filters for the airbox have a large surface area, as do the ones for use without the air box, (mikes, Kenny Roberts pic, although as established not in use with CV carbs), I think that has to b taken into account. Mike'sXS's pleated filters have a reasonably large surface area. XS Johns air box mod required him to up the mains to compensate for more airflow. To my uneducated mind, those small pods just don't allow enough air.

I wonder just how much the small pleated skirt problem has been carried over to the large pleated pods just because.

 

[gggGary]

Not to disparage Yamaha's racing team but um that was the 1970's y'know 50 years ago.
They were running round slide carbs too.
modern competitive bikes stock or race with round slides? birds chirping.

https://www.ducati.ms/threads/airbox-volume-effects.29853/
https://ducatimonsterforum.org/index.php?topic=4736.0



This is running VERY well with CVs and small (but not cheesy) pleated pod filters...

got it back together and fuel tank FINALLY is clean inside, 40 smiles today
It'll blow the doors off about any XS650 ever. The gro/howl of the intake as she blows through 8G is awesome, it's a quiet pussy cat down low, impeccable manners.
I've got the stock airbox and it's going back on.
Late 90s up YZF 600 carbs

Velocity stacks that separate the float and slide chamber from the intake flow/pulses sitting inside a large volume airbox.

A view inside an EBR airbox they threw all kinds of stuff inside the air box in a quest to keep it's volume as large as possible.

Volume on the Uly airbox must have been a priority also, it's BIG.
more ducati guy talk airbox volume talk.
http://www.desmoducati.org/airfilter.html
some more
This is a good place to begin- http://www.thunderproducts.com/AirboxesDynotech.htm

More, with math- http://motorcycleinfo.calsci.com/Airboxes.html
I started an airbox heimholtz resonance thread long ago interest in it was nil.
Yo-mama found 10 HP for the 1300 V4 Venture motor by adding a long intake tract with air filters about 16" from the carbs (they were out in the fairing lowers.)
Madness with VMs has the biggest UNIs I have room for tween carbs and airbox the last set made it about 10 years and were only replaced when I changed the crankcase vent set up to a reed valve.
I keep the side covers cuz I worry about wet filters flooding the motor in a rainstorm.
Gonna go kick on the TX650 for a while.

 

[Jim]

The gro/howl of the intake as she blows through 8G is awesome,

You jus' sent a chill down my spine....

 

[5twins]

The K&N pods I started out with were basically the same size and shape as those MikesXS Performance pods. They didn't block any of the ports in the bell mouth and I know they were large enough because they are the same part number I used on my Moto Guzzi LeMans 1000 w/ 40mm Dellorto carbs. I started out on the MG with pods that were too small. A quick test run with them removed proved that point - the bike ran better and made more power ......

I've read many times on the forum here that the factory airbox is best. I didn't find that to be true when I eventually got to try one. My '83 came to me with one so I kept it on there for a couple of seasons just to see, lol. But, eventually I couldn't stand it anymore and put UNI pods on. This was mostly a "convenience" thing. Those factory airboxes hog so much space under the side covers (basically all of it, lol), are difficult to remove and install, and make accessing the carbs and removing them much more difficult. Now, I can't say the bike runs any better with the pods, but it certainly runs no worse. Like I said, it was mainly a "convenience" thing. The only downside I've encountered with the pods is if you get caught in a heavy downpour. When you come to a stop, the pods may suck some water in. The bike can start running rough and even stall if you don't keep it going with some throttle blips. At speed, this isn't an issue, I guess the water blows by.

 

[BluzPlayer]

Not to disparage Yamaha's racing team but um that was the 1970's y'know 50 years ago.
They were running round slide carbs too.
modern competitive bikes stock or race with round slides? birds chirping.

You're right Gary.
Those are round slides.
I have round slides for mine.
I understand the operation of the CV and how it uses the differential pressure to operate.
I understand the airbox and how it delivers more even pressure to reduce the flutter.

The 900F takes me back.
Back in 1977 I bought a new Honda 750F.
I had considered the xs650 but the performance levels of the bikes wasn't even close.
It ran like a beast and handled well.
CV carbs and I kept the airbox.
Couple of years later I put a RC Engineering 1000cc kit on it and upgraded the suspension.
Readjusted the carbs and went with pods to get more air. Bike always ran great.
Never missed a beat and was a pure pleasure to drive. And yessss... the throttle had full response. I still miss it. I have no doubt that 900F you grabbed will give you many grins.
I even considered taking up a project 750 to build before deciding on the XS platform for the reasons I gave in my introductory thread. No regrets on the decision.
Crazy how I picked that 750 over the xs650 back then and 40 something years later I went the opposite direction. I ride different now.
I fell in love with the easy ability to modify the xs.
I didn't mean to derail... so apologies.

 

[gggGary]

Some more on airboxes, intake tracts.
https://www.advrider.com/f/threads/airbox-design-and-resonant-tuning-of-the-airbox.1352551/
When I got madness it was set up for 5K to redline and it was tricky shifting before it blew through 7500
Fun on the street? Nope it was a dog BELOW 5K. Bigger quieter mufflers, and smaller carbs (VM38's down to VM34's) made it a MUCH more enjoyable ride, broader more USABLE powerband with plenty of go for the old guy.
I've thought about putting madness back to her "Race motor" set up and ride a different XS for most street use. Would make a good spot for a high flow head.

 

[GLJ]

When I got madness it was set up for 5K to redline and it was tricky shifting before it blew through 7500
Fun on the street? Nope it was dog BELOW 5K

Wasn't fun then it still won't be now. Horsepower is great. It has to be usable. I seem to remember reading that when Yamaha was was racing the 650 they found that 72? horsepower was the max that he engine cases could handle. Then they quit going for more horsepower and tailoring the engines for the riders styles.

 

[BluzPlayer]

Would make a good spot for a high flow head

Lol..
I know somebody...
I'm working on a process now that I derived from testing in the D Port Report thread that I believe will be even better tuned.. more consistent...
Not just between the 2 ports of a head, but between different heads. I believe it will be the best process for increasing the performance.
Possible for the three main flavors:
650,700,750.
I'll be introducing it soon and expect to be prepared to offer a head or the service on a member's own head around fall. (2 week turnaround). I can still do the work for somebody that doesn't want to wait or has a previously modified port. but I am certain that the new process will be the best option.
Sneek peek coming in the D Port Report this weekend as I cover the port's design.

I've got numerous formulas regarding resonance wavelengths and intake tracts.
Optimization of that is on the back burner.
Just too much on the plate for the moment.

 

[Jan_P]

Not done the readup And dont know Much about carburation
But have worked with Air Condition

Thinking out loud here.
If I recall right the stock air boxes are sucking in air from the sides .. in direction towards center
Turning the flow 90 degrees. To the motorcycles longitudinal direction
Not much air coming in from the center.
But there is a connection pipe between the sides ..

There is a thought process here .. One side is on the work expansion stroke aka Closed valves and the other sucking in aka Open
If I am even close here.
That is a Complicated Flow situation
And a situation that have restrictions over the Rev range + Fuel Economy + Noise + Pollution

It may well be an uneven airflow entering the carburetor but one that the Yamaha Engineers have taken into account for the
Complicated Carburetor Multiple Air Jets ..Multiple fuel jets

But with the Pods or so is there not a suction of air possible from the center outwards
Air that both cylinders compete on to get. First
And these flows collide so to speak .from center out and out in
Something Yamaha Designers .not taken into the design

On the stock set up .removing the filters turning the flow 90 degrees would have effects
Secondary flow .. Maybe also with filters there..

I dont believe there is anyone able to figure it out at the desk Lots of trial and error .And the Filterholders have evolved
Getting it right with Pods is not certain at all Maybe can happen

As mentioned here the Racers typically don't have the restrictions above Noise / Economy some even use overfueling for Cooling
And typically dont care about low rpm performance .. It they can find a Sweet spot .With High rpm they are gonna Use it

Perhaps the aftermarket have got it right together .But it is not straightforward And involves complicated rejetting head scratching.
I know of one getting it wrong .To lean and Shot his motor.

This brand is a large company and have manufactured bikes for many years .At that time very good Quality attention
On a bike evolved over ca 15 years Those people are experts .. Need to be careful

 

[AUTOMAN]

Not done the readup And dont know Much about carburation
But have worked with Air Condition

Thinking out loud here.
If I recall right the stock air boxes are sucking in air from the sides .. in direction towards center
Turning the flow 90 degrees. To the motorcycles longitudinal direction
Not much air coming in from the center.
But there is a connection pipe between the sides ..

There is a thought process here .. One side is on the work expansion stroke aka Closed valves and the other sucking in aka Open
If I am even close here.
That is a Complicated Flow situation
And a situation that have restrictions over the Rev range + Fuel Economy + Noise + Pollution

It may well be an uneven airflow entering the carburetor but one that the Yamaha Engineers have taken into account for the
Complicated Carburetor Multiple Air Jets ..Multiple fuel jets

But with the Pods or so is there not a suction of air possible from the center outwards
Air that both cylinders compete on to get. First
And these flows collide so to speak .from center out and out in
Something Yamaha Designers .not taken into the design

On the stock set up .removing the filters turning the flow 90 degrees would have effects
Secondary flow .. Maybe also with filters there..

I dont believe there is anyone able to figure it out at the desk Lots of trial and error .And the Filterholders have evolved
Getting it right with Pods is not certain at all Maybe can happen

As mentioned here the Racers typically don't have the restrictions above Noise / Economy some even use overfueling for Cooling
And typically dont care about low rpm performance .. It they can find a Sweet spot .With High rpm they are gonna Use it

Perhaps the aftermarket have got it right together .But it is not straightforward And involves complicated rejetting head scratching.
I know of one getting it wrong .To lean and Shot his motor.

This brand is a large company and have manufactured bikes for many years .At that time very good Quality attention
On a bike evolved over ca 15 years Those people are experts .. Need to be careful

it's a 360 firing order, 360 intake event.
how does the air compete?