All text & images © The Flying Banana, 2006.

Air Filters...

Probably one of the most often overlooked aspects of engine tuning and maintenance, is the AIR FILTER. An air filter element may look clean, but in reality it can be clogged to the gunnels with dust, causing your engine to run rich and fuel economy to drop through the floor. Worst of all, you lose power — no laughing matter. So no one needs to tell all you good boys and girls out there to change the air filter at the stipulated service intervals, do they.

Suzuki OEM air filters are excellent filters, but as you may have noticed they are rather expensive things to toss in the bin every 12 months or so. What to do?

Well a few months ago I invested in a UniFilter for my GS(X)1100 Katana (product tag here). In terms of filtering the air I'm sure it was doing the job... but when it came to getting the thing in and out of the air filter box, it was an absolute pig. There is no nicer way to put it. I am sure that for other machines, etc. the UniFilter items fit very well, but it has to be said that for my GS(X)1100 they cannot be recommended in their current form.

So it was time to take matters into my own hands. Now this solution may not be to everyone's preferences, but in the end I decided to build myself a new filter using the old OEM filter frame. Whatever happened, at least the dimensions would be spot on!

Here's how you do it...

[But before you go any further, please read The Unfortunate But Necessary Disclaimer.]
  1. Carefully cut out as much of the old air filter element as you can using a sharp knife.
  2. Burn out the remainder of the element, as well as the glue that was used to hold it, using a blow torch. And yes, this is fun but you really should do it outdoors...
  3. Now you will be left holding three metal pieces: the perforated central 'cage', and the two end-pieces.
  4. Clean, scrape and wire-brush them so that no soot, charcoal etc. remains.
  5. Using a file or a grinder, take away the galvanised coating from either end of the 'cage', and from the points on the end pieces where they are met by the edge of the 'cage'.
  6. Solder it all together. It's best to 'tin' the surfaces first with soldering fluid and solder, using a blow torch to heat things up, and not a soldering iron.
    (If you don't have the skills or equipment for soldering, you should be able to achieve a bond using epoxy resin. Or, you could even use the same contact adhesive that you'll be using below. But I cannot vouch for either of these methods, as I haven't tried them.)
    Anyway,this should be what you have now:

  7. If you haven't done so already, wander off to your local foam retailer, and ask for some air filter foam. You want foam with a reasonably small pore size — have a look at other foam filter elements for a guide on this. (DO NOT use ordinary cushion foam or anything like this, because it does not allow air through.) You want a piece of foam that is about 250mm long, 150mm wide, and 15mm thick, as well as another smaller piece to create the seal at the 'mouth' of the filter where it butts up to the inside of the airbox.
  8. Using a contact adhesive (I used some snot-yellow goop called 'Selleys Gel Grip'), coat the ends of your rectangluar piece of foam, and begin to position it around the filter cage, thus:

  9. Carefully push and pinch the surfaces together, taking care to align them evenly along the length of the seam.
  10. Once the seam has taken a set, slide one end of your filter foam 'sleeve' back from where it butts the metal end piece, and apply a coat of adhesive around the end of the filter material, and also the inside surface of the metal end-piece. Carefully push the sleeve up to the glue-coated metal surface, and push and press it into contact.
  11. Repeat this last step for the other end of the filter 'sleeve'. Now you should have something that looks like this:

  12. Finally, make a foam seal for where the filter 'mouth' will butt against the inside of the air filter box. Use the end of your filter as a template. Then glue it onto the end of your filter using the contact adhesive. It should now look like this:

  13. Allow the contact adhesive to take a final set for a couple of hours in a well-ventilated area.
  14. Now you are ready to impregnate your new filter element with filter oil (which you can purchase from any motorcycle store). Work the oil into the foam — not forgetting to oil the foam seal at the filter 'mouth' — and squeeze out the excess. Leave it to dry in the open air for an hour or so.
  15. Install it into the air filter box and voila, your bike can now breathe again without getting dirty lungs.

A couple of things to note...

  • Now it's all very dependent on how your bike is currently tuned, but please note that oiled foam air filters usually allow significantly better air-flow than a stock paper-element filter, so your engine may run a bit leaner. Usually this won't be a significant problem... but it might be, especially if your engine is already running on the lean side. So... be aware.
  • The service interval for your foam air filter element will be comparable to other oiled foam filters. To clean, wash the element in mineral turpentine. DO NOT soak the element in petrol, as this will dissolve the contact adhesive.

Dual pod filters for the GS1000

If you've ditched the airbox for whatever reason (and there at least a couple of good ones, 1/. better breathing, or ii/. making carbie removal, servicing and adjustment soooo much easier), then aside from velocity stacks you will be considering POD FILTERS. These marvellous things are widely available online. And they are usually fairly expensive, too... K&N are probably the pick of the bunch. A bit cheaper are the 'RamAir' jobbies, but if you ask me they just don't fit well at all, tending to foul eachother between carbies 1 & 2, and 3 & 4. 'Emgo' pod filters are the cheapest, and they fit properly. The thing is though, I wouldn't trust them to do a good job in the long term. For one thing, hold them up to the light, and you will see lots of small (and some not-so-small) sparkles of daylight shining through. For another, they really are a throw-away item, not made for cleaning and re-oiling.

What to do? Well, what I did was take the old 'Emgo' filters, separate their metal flanges with their rubber manifolds from the rest of the filter (which I chucked in the bin), and use these flanges etc. as the basis for making a pair of 'dual' oiled-foam pod filters for my GS1000. For filter foam I ordered some 200mm x 300mm 'RamAir' foam sheets via eBay (2 sheets will be plenty for the job), and set to work with a tube of 'Selley's Kwik Grip' contact adhesive, a pair of scissors and a *sharp* box-cutter knife. Here are a few photos which should be self-explanatory:

You'll notice that I"ve 'flattened' off the end of the flange there. This is because otherwise the filter sticks a bit too far out to the outside, and will rub on the inside of your trouser leg, earning you all sorts of curses and epithets from your washer-person. As the said washer-person is usually also the permission-giver for all 2-wheeled purchases, we do not want to make her work in the laundry more difficult, do we. QED.

Once you've left the glue to set properly overnight, you just oil them with foam filter oil, squeeze out the excess, and then press them with clean rags until the excess is gone. What you are aiming for is oil-coated foam without the cells in the foam being filled with oil... so that the air can be drawn through, dirt particles are trapped by the oil film, and nice clean air gets through to your carburettors. As I've pointed out above, when the time comes to clean them, use mineral turpentine (aka 'parrafin') and not petrol/gasoline, as this will dissolve the glue you've stuck the foam together with.

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The Unfortunate But Necessary Disclaimer:

All of the information here is for you to weigh up and use AT YOUR OWN RISK. While I have taken great care to ensure that the information on this page is accurate, YOU are the one who must judge whether the information in this article is correct and applicable to your machine and circumstances.

Furthermore, I am not a mechanic or engineer. I have no related qualifications and I am not endorsing, recommending or advising in any way. I strongly recommend that anything on this webpage be discussed with your local mechanic before any action is taken to implement the content of this webpage. So there.

Not only that, but YOU ALONE are responsible for any injuries you may sustain in attempting the procedures described on this webpage. You will note that cutting yourself with the knife, or burning yourself with the blowtorch, or even burning down the shed and the house, and all other such stunts, are not mentioned in the procedure. So do not do them, and do not blame me if it all goes pear-shaped.

Oh for a world without wretched disclaimers.

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