K&N vs UNI air filters on non-CV carbs (VM/TM/RS/CR/PWK, etc)

[arcticXS]

Guys,
I understand that the consensus is that oem CV carbs on the XS work best with UNI filters.
But is there any difference if non-CV carbs are fitted? I have a pair of linked 34 mm Mikuni flatslides on my XS, and are currently using tapered oval K&N filters. The bike runs great, starts easily and idles smooooooth. I have a set of UNI filters I haven't tried yet, that require a short adapter tube, maybe 40 mm or so. The carbs have a 55 mm OD, and the filters are 63 mm ID.

I am also planning to remove the stock battery box next winter, since I am using a much smaller battery. This will allow me to try some velocity stacks between carbs and filters, maybe as long as 4 to 5". I hope this may improve the torque curve somewhat, utilizing the "third harmonic" of the intake duct. I guess around 10" from inlet valve to end of stack can be a decent starting point. But that is for winter...

 

[gggGary]

Personal opinion is that the UNIs provide better filtering, I've always been turned off by being able to see light through a K&N.

 

[arcticXS]

Personal opinion is that the UNIs provide better filtering, I've always been turned off by being able to see light through a K&N.

I'm not too concerned about that. I have a Ducati 600/680 that has run near 100 000 km with a flat type K&N in the stock air box, with snorkels removed. And used K&N filter in 2 BMW cars for over 500 000 km total, with no ill effect at all. None of the cars were burning any oil at 250 000 km mileage. But then I do not exactly live in the desert either, we mostly have dusty conditions in early spring only, due to winter sanding of icy roads. On my RD350 I also use a single, large K&N, replacing the entire air filter box, but still using the original rubber "Y-boot" between carbs and filter. On that setup, I also use a "Drycharger" sock over the filter, mainly to keep rainwater off.

What I try to find out if there is any significant difference in jetting requirements and/or engine power between UNI and KN filters, all things being equal (filter area/ dimensions)

 

[copernicusdan]

Has anyone tried them on Mike's xs carbs?

 

[TwoManyXS1Bs]

Something to consider is the way the bowls are vented.
On the XS650 BS38 CV carbs,
70-77 bowls are vented to the atmosphere.
78-79 bowls are vented to the intake horn.

The 78-79 carbs would be more immune to filter restrictions.

Back in the day, I modified my VM36 carbs to bowl vent to the intake horn...

 

[RC4MAN]

I've used each in various applications and personally prefer the Uni's for ease of maintenance and durability.
A heavy hand will quickly ruin a K&N and make gaps big enough for easy dirt migration.
I bugged Uni enough they finally built a unit for my V-Rod and gave me a free trial unit with maintenance kit as long as I would report on the V-Rod forum.
I've had it in 12 years now, it gets serviced yearly and is still in great shape.
It's interesting to note that all dirt bikes that I know off offer foam filters as original equipment, and even HD offers an alternative fiber filter element for their Screaming Eagle upgrade kits rather than a pleated gauze.

 

[XSLeo]

I like the foam. I use the Uni's on my 75. On the 81 and 83 the stock filters had the aged filter media pretty crappy. Torn and crumbling apart.
I cleaned of the old stuff. They can fall apart when doing this. Not a real problem. JB Weld fixes that. Once clean and glued back up I ordered some 3/8's thick green foam filter sheets. Cut pieces of the sheet just a bit wider than the old filter cage/screen area and long enough so it over laps once wrapped around the cage.
With the foam properly oiled just wrap around the filters and slide in place. I left the foam full length of the sheet so the over lap is about as long as one side. I wrap so this doubled area is toward the inside. No need to tie the foam around the cage.
Works well and when time to clean just just slide them out, the foam unwraps and cleaning is easy.
I like easy.
Leo