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Jun 14, 2003
Have you ever held a K & N air filter up to a bright sky? You can actually see tiny bits of sky through the weave in many areas around the filter. I would assume that a slightly smaller dust particle could whistle right through these holes and head straight for the cylinders walls where it would act like an abrasive.

Does anyone know if there are other options beyond the stock filter/air box combination and the K & N filter?
Jason, Have you seen the truck test were a fleet of trucks all got sand in their motors? Why do ya think they flow so good? And need lots a oil, and are a better filter dirty than clean. Oh man get the scoop.

There seems to be plenty of evidence to strongly suggest that K & N filters do not perform as well as most stock paper filter elements. The question then becomes: what is a good alternative?
Jason, I run Norvil velocity stacks on one of my bikes and I have fabricated a clip to hold a tea-strainer type mesh over each bell-mouth. These really only prevent the ingress of small children and dogs, but I have found that a foam cover for a 'Sure' SM 58 microphone, fits perfectly and with a bit of air-filter oil has proved serviceable for a few years now. They are also very reasonably priced from most music or Hifi shops, although some of the really cheap generic ones are a bit on the flimsy side.
Jason Curtiss said:
what is a good alternative?

Oiled foam. Dave's solution is certainly creative and it sounds like it works ok. On my old 850 I used Unifilter foam socks that clamped onto the Amals. They were cheap, seemed to filter well, and were easy to fit and remove for cleaning. They didn't look as flashy as a fancy K&N unit, but probably (don't know for sure) filter better. Oiled foam has been the standard for dirt bikes for decades.

I currently have K&N filters for both of my Nortons though :oops:

I've held the front wheel up to the bright sky!!!!!!!
as for the filters if treated with correct oil and wash at the correct interval
with the correct K&N service kit you won't fit better. No I don't work for them
I use K&N filters on all my bikes (currently Ducati, Harley, Norton, and Triumph), and swear by 'em. I just added an airhead BMW to the stable, and so have been treated to lots of criticism of K&N by that crowd. I'll be fitting K&Ns to that bike as soon as I take delivery.
Oh man just be sure the first bit of dirt that goes on that oiled filter is clean dirt.... I run them on all the bikes as well unless I can find the nice paper ones for a lawn mower...
Has nobody else ever tried K&Ns and been dissatisfied ?

I had one of the single units that fits both inlets on an 850 and could never really disguise an upper mid-range flat spot. Raising the needle or bigger mains disguised the symptoms but only at the expense of producing others.

In my opinion, the best option for power and pick-up is velocity stacks with extended inlets followed by stacks on the standard tracts.

For all-round running, the 750 air box with paper element takes a lot of beating - It is efficient and doesn't seem to produce any adverse effects.

Anybody want to buy a K&N that's been in a drawer for 20 years ? :)
I'm on side with you 79x100, I run a K&N on my JPN just because it was on when I bought it, never managed to get it sweet at the top end. I have a Guzzi Le Mans Mk1 which runs open bellmouths (Gauze you can get a chicken through) over 60K miles, no wear on the bores!! I run Mikuni's on 2 Commandos with paper filters & std on 2 Standard is good I think. But at the end of the day K&N's are easy to remove and save the cursing with the original set up (especially paper pre 74 air filters) Whatever you decide you can argue your case I thinl. :)
K&N is just a throw back to the early years of oil/mesh filters. They are good for the wanna be go fast crowd. There is a stock FRAM filter that fits perfectly on the Norton. I have 3 K&N,s in my junk box if anyone wants one.
This is another one of those religion, politics, oil & tires discussions.

All positive results from all others aside, what the intake wants most is clean, free air in the largest available quantities. Then, it is up to the tuner to properly meter and moderate the fuel and air mixture according to the air intake configuration he is dealing with.

I just can't see putting clip-on screens on bellmouth velocity stacks, that only disrupts the air at the most critical point (the tuned, curved entry mouth). What you want to do is surround the opening with a filtered-inlet enclosure so that the air immediately surrounding the opening of the intake is totally free to flow in a smooth manner. This is the description of an airbox.

Also, when you employ a standard airbox/filter arrangement, the filtering media surface area is typically many multiples of individual filters, so it takes longer to cause ill effects from clogging.

P.S. Add my name to the "likes dual-mouth K&N filters" list. They are essentially a smallish airbox.
I originally had a K&N filter that fit the standard air box. I ditched it, but not because of performance. The unit was slightly deeper than the standard paper element and it made it very difficult to get the filter out to work on the carbs. After tearing up 2 sets of carb hoses and a lot of frustration, I threw away the K&N and went to the standard element.
Yup, that's why I went with the clamp-on K&N. My 750 came with the stock airbox and a K&N filter and it was an incredible PITA to get the filter in and out. I was wondering if it was a little deeper then the stock filter because it certainly didn't seem to fit very well.

That's another item residing in my useless spare parts box now!

Grand Paul has it right a custom air box would be ideal. Read huge air filter. But I did find a way through that works and uses K&N with mark 2's a little notch in the oil tank and bam your done takes about a table spoon of oil away.
I use a pair of S&Bs on my Mk2 Amals and they give a little more room. What "rubber" tube are you using on the manifolds? I find the Amal tube softens over time.

The FRAM filter to use with stock 71 air cleaner is CF146. It is a round filter but curves just fine.
Satisfied with what I have. 27 years, 120,000 without the pistons replaced or bottom end being apart. Only rings replaced, same bore size. I wouldn't change for those funky things.

Check out this info:

broken link removed


This is something you can build yourself...wire mesh and a bit of soldering.
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