F650 Airbox and Filter FAQ

compiled & edited by Kristian #562
Please read the Disclaimer before attempting any work in this FAQ.
Last Updated: 30 December 2006, by Winter #1935

Introduction
Filter Cleaning
- Alternative 1
- Alternative 2
Aftermarket Air Filters
Questions
- When I get a new foam filter, do I need to Oil it?
- What is the Airbox drain tube for?
- What is the Airbox drain tube for?
- How does the oil from and overfilled oil tank get into the airbox?
- What route does it take?
- Under what circumstances does the oil actually get down the beather pipe/s into the airbox?
- How do I check if the breather is getting submerged?
- How does fuel get into the Airbox?
- What are those 2 hoses on the Bottom of the Airbox?
- Will and aftermarket filter improve performance?
- Do I need to re-tune / re-jet my Classic F650 with a new UNI foam filter?
- Are there any alternatives to air filter oil?

For other related FAQs:

Introduction

The Airbox and airfilter are important parts of your bike. Clean air improves the combustion process, and the airbox helps reduce the noise from the engine. Keeping your filter in good condition helps with the combustion process, and checking the airbox can help identify problems with the bike (such as too much oil).

The other thing to keep in mind with the airbox, is this provides the air intake into engine. This is important when going through water. If the water is below the air intake, in theory you can cross it. The intake location on the GS/Dakar is much higher than the Classic models.

Filter Cleaning

Cleaning Alternative 1

by Kristian #562, 15/10/01

Removal

Remove the Seat.
Remove the LHS Body Panel (2 Allen Key Bolts), 1 Pull-out Plastic Nipple in a Rubber Grommet
To the rear of the battery, just forward of the Exhaust Crossover and beside the LHS rear of the Airbox there is a 2" wide by 5" high Plastic Plate held in Place by two Small Bolts which fix into the Airbox. It looks like this: Air Filter Location The Bolts have about 8mm Heads. The Plastic Plate also has some "Electrical Stuff" attached to it, that looks like a short cylinder. (Flash knows exactly what it is, but I believe it's a solenoid).
Undo both the Bolts and using the attached Wires as a Hinge, gently bend the Plastic Plate (With Wires attached) to the left, toward the battery.
Behind this Panel is the Air Filter, which sits in a groove and just slides out. Air Filter Exposed Wear cotton gloves, it is sticky!
Make sure you note which way UP the filter goes as at the RH end there is a non-symmetric curve.

Cleaning

Remove the Air Filter from its Plastic Frame (Yes you can prise it apart). Air Filter Removed
EITHER, using petrol or bike cleaning agent soak the Filter for 5 mins then squeeze and repeat. Rinse the Filter several times with water until it runs clear and there is no sticky feeling left.
OR soak overnight in a tub of Washing Powder and then rinse the Filter several times with water until it runs clear and there is no sticky feeling left.
If you have a can of spray on filter oil spray it one to cover all surfaces and then put filter in a Zip-Lock Bag and work the oil through. Squeeze out any excess and reinsert in Frame.
Otherwise put the Filter in a Zip-Loc bag with about 1/4 cup of Filter Oil and work the oil through thoroughly. Squeeze out any excess and reinsert in Frame. Make sure the holes match up, don't put new holes in the Filter.
Installation is Reverse and be careful you don't tighten the bolts too much. It's Plastic. That's it. Easy & Cheap!

Cleaning Alternative 2

by Flash #412

This is the diagram to consult.
Remove the two screws and pull off the left sidecover. The solenoid is not in the diagram (to the right of the battery). It is attached to the cover and can be left in place.
Remove the screws that hold the cover, number 4 in the picture.
Pull the filter assembly out. 5 and 6 can be popped apart.
Remove the foam. Clean the foam in detergent and warm water.
Unless someone has used the other kind of filter oil, that should clean it.
If it doesn't immediately work, try mineral spirits.
After you get it all clean and rinsed, let it dry completely.
Get some water-washable filter oil and follow the directions.
Let the oil "set" completely. Reassemble in reverse order.
It is pretty obvious how the foam goes back in the rack.
And the assembly only goes back in the housing one way.

Aftermarket Air Filters

compiled & edited by Kristian #562
edited by Nick # 1085

K&N Filters

K&N Part Numbers
Item	Classic BMW F650 US	F650GS/Dakar
Stage 2 Jet Kit	81-9326	N/A
Oil Filter	KN-151
Air Filter	NM SQ-2875 (BM-0001)	BM-6501

FactoryPro on K&N Filters
Hi Kristian, > Kristian wrote: > > Hi. > > 1. Do you have any feedback from anyone about the size of Factory > Jets people have used with a Staintune Pipe and Standard > K&N Filters and the needle clip location? Pretty much, no. We get virtually no feedback, complaining, praise, brickbats, etc.... from F650 guys. I have to assume that all is well with jet kit / F650!! > 3. How much is the Factory Jet Kit for the BMW F650 1996 Model and > what assortment jets/needles does it contain? There's pilot jets, needles and a selection of main jets. I don't know, off the top of my heard, exactly which jets are included. We do have more jets for sale for a larger spread if you think you might need them. Cost: $79.95 Shipping to Hong Kong: $20 > > 4. Some people reckon the K&N Air filters let too much crud through and the valves are shot pretty quickly. What filter do you recommend with this kit? Umm, at the risk of sounding pessimistic, an oiled foam filter filters really well. If I was using my bike in a dusty area, I'd not use a cotton gauze filter..... But, I'd expect that there's not much dusty wilderness left in Hong Kong? What usually happens is that the valve seats get carboned up.... Silt in the engine, I'd worry about rings.... Cheers! Marc > > Thanks & Rgds > Kristian -- Marc Salvisberg email: factory2@ix.netcom.com Factory Pro Tuning http://www.factorypro.com/home.html Factory Pro Dynamometer http://www.factorypro.com/dyno/indexdy.html

FactoryPro on K&N Filters

Hi Kristian, 
> Kristian  wrote:
> 
> Hi.
> 
> 1. Do you have any feedback from anyone about the size of Factory
> Jets people have used with a Staintune Pipe and Standard 
> K&N Filters and the needle clip location?

Pretty much, no. We get virtually no feedback, complaining, praise,
brickbats, etc.... from F650 guys. I have to assume that all is well
with jet kit / F650!! 

> 3. How much is the Factory Jet Kit for the BMW F650 1996 Model and
> what assortment jets/needles does it contain?

There's pilot jets, needles and a selection of main jets. I don't know, off the 
top of my heard, exactly which jets are included. We do have more jets for sale 
for a larger spread if you think you might need them. Cost: $79.95 Shipping to 
Hong Kong: $20

> 
> 4. Some people reckon the K&N Air filters let too much crud through
and the valves are shot pretty quickly. What filter do you recommend with
this kit?

Umm, at the risk of sounding pessimistic, an oiled foam filter filters really
well. If I was using my bike in a dusty area, I'd not use a cotton gauze
filter..... But, I'd expect that there's not much dusty wilderness left in
Hong Kong? What usually happens is that the valve seats get 
carboned up.... Silt in the engine, I'd worry about rings....

Cheers!

Marc

> 
> Thanks & Rgds
> Kristian

-- 
Marc Salvisberg email: factory2@ix.netcom.com
Factory Pro Tuning http://www.factorypro.com/home.html
Factory Pro Dynamometer http://www.factorypro.com/dyno/indexdy.html

Unifilters

Twin Air Filters

http://www.twinair.com/

Looking for a better filter and having had wonderful success with an ITG foam filter on my '97 M3, I wanted one for my GS. I came across several IBMWR and Gang members that recommended Twin Air foam filters. Unfortunately, they were all non-US members, and the US Twin Air distributor was not easy to find.

Anyway...They're here, they're nice folks and they do have custom foam filters for the F650, which they tracked down from their manufacturer in Holland ('05 GS part# 158304-F, $44.95 ea). Just wanted to pass along their phone #, in case anyone else was interested: (215) 258-5124 Patterson

Opinions

Any air filter in a dirty environment will require maintenance. The K&N, as others, may require a pre-filter in the heavy silty stuff. Most of the factory off-road teams use K&N (here in the USA). The K&N will not increase horsepower. Rather, when compared to the stock filter, it will increase airflow to the carbs. To increase horsepower, one must add gas to the mix; thus a needle and/or main jet change might be needed. Ramey.
Driving without air filter. There is not much to worry about running w/o filter long enough to troubleshoot jetting. Like Richard said they used to run motorcycles for years with nothing more than gravel strainers on the intakes. There is only one size of particle that does any damage when it gets sucked in and blown out of a 4 cycle engine (two strokes are a whole different story!). I don't know if you have a paper element or not but if you do you should consider a change right away if you do. Paper is not a good filter medium for many reasons, one of which is it swells up when wet with water or oil fumes and doesn't pass any air. It's like riding with choke on. I recommend K&Ns but I don't want to start that debate here again. F650McGyver
If you stay out of dust storms and locust swarms, you should be OK. The British and Italians have ridden their motorcycles around for years without air filters. It wasn't until the 1980's that they discovered them. Richard #230.
I have switched back to the stock airbox. Mainly because the K&N Oval setup is really loud. Doug, '99 F650, Cleveland, GA, #1206
1. I've read your FAQs re the air filter and snorkel. Being in Australia, you can't get the K&N parts readily (some are on order, but for US$60, I'm not interested). So I've tried something different. I bought some filter foam, cut it to the size needed, keeping the rubber seal of the original filter (which acts as a spacer) and cut out the old paper filter from around the seal.
2. Fitted the foam filter with filter oil into the cut down snorkel housing (meaning the filter element was in a different place - forward of the original filter position but at the rear of the cut down snorkel). Some gasket sealant to build up a flange and help the seal was added to the rear of the snorkel housing.
3. The result? Better air intake, and any worries about water etc into a paper filter are now history. Plus, if conditions are a bit dusty (which they are in a drought which we have in Oz right now) I can clean the filter foam without worrying about finding spare parts on the road.
4. For US$10, with spare filter foam left over, I'm happy! I'll monitor its performance and check the filter regularly to make sure there are no signs of dust, dirt, insects etc getting around it, but it looks like it'd work well.
5. Cutting the snorkel (which increased the size of the air intake) made a huge difference to performance, I was wondering why the Staintune I fitted made little difference, but you can't breath OUT until you can breathe IN I guess :) Hopefully the new filter might also make a difference. Ross F650, Dakar, Brisbane. Australia.
6. The home made filter didn't work too well, but I may try again.
Air Filter - K&N Air filter BM-6501. This air filter is worth investing. The filter is washable and it comes with a foam insert. If using Staintune pipe is better without the foam.

K&N Air filters: K&N Air filter BM-650. scx
Remember tests show that while these filters flow more air the air filters are not as efficient as the stock paper element.
Letter from Rick Blum, Technical Support Supervisor, K&N Engineering

This was a letter sent to the Editor at Ford-Diesel.com from Mr. Rick Blum, K&N Engineering Technical Support Supervisor. This letter was sent to help counter misinformation and conjecture that was observed on the Ford-Diesel.com forums concerning the K&N air filtration line. - andy112652

Dear sir,

I work at K&N Engineering and have been receiving a lot of questions regarding our product's integrity, reliability, and effectiveness from information posted in the Ford-Diesel.com forums. It seems these forums contain a lot of opinions and not a lot of scientific testing or factual data. I would like to provide some information to you and your readers regarding the K&N product line.

K&N filters are tested by an outside, independent laboratory, Southwest Research Institute in San Antonio, Tx. They have been proven to stop at least 99% of particles on a SAE dust test. This test uses a range of particles from the 0 - 5 micron range up to 20 microns. For comparison sake, a paper filter stops 99% on the same test and the OEM minimum standard is 96%. Foam is generally the worst media with a typical efficiency rating of 80 - 85%. To get higher ratings, the foam must be more dense and consequently more restrictive. The "tack" characteristic of a K&N allows for increased filtration without loss of airflow.

The testing procedure used is SAE J-726 using ISO Test Dust. This test is the standard of the air filter industry. The test procedure consists of flowing air through the filter at a constant rate (airflow rate is determined by the application) while feeding test dust into the air stream at a rate of 1 gram per cubic meter of air. As the filter loads with dust the pressure drop across the filter is increased to maintain the prescribed airflow rate. The test is continued until the pressure drop increases 10" H2O above the initial restriction of the clean element (in this case .78" to 10.78" H2O). At this point the test is terminated. The dirty filter element is then weighed. This weight is compared to the clean element weight to determine the total Dust Capacity. The amount of dust retained by the filter is divided by the total amount of dust fed during the test to determine the Cumulative Efficiency.

* The K&N filter achieved the following results:
Dust Capacity 305 Grams
K&N Cumulative Efficiency 99.05 %

*Links to the filtration tests are on the K&N web site at:

http://www.knfilters.com/images/factstab1.gif

http://www.knfilters.com/images/factstab2.gif

So, what this proves is that you really cannot arrive at any intelligent conclusions by holding the filter to the light. That inspection is useless, pin holes are normal. In fact, those pin holes are what makes a K&N filter efficient. Within those holes, there are actually hundreds of microscopic fibers spanning them. When treated with oil, these fibers capture and hold the very fine particles. On the same hand, the fibers allow the filter to flow more air than paper or foam. Additionally, we have to understand that oiled fibers are translucent and are not easily visible to the naked eye. Spray some WD 40 on a sheet of white paper and you will see the effect. The K&N filter is four-ply cotton gauze unlike some competitors synthetic material filters. The synthetic material filters do not have the very small fibers that natural cotton does. Also, the oil in a K&N is completely absorbed into the media and there is no risk of contaminating electronic sensors as there is with Foam filters that can have oil pulled from the soaked media.

K&N got started over 30 years ago making filters for motorcycles and off road racers. The filters did so well that these customers wanted similar filters for their cars and trucks. K&N started making filters for these applications and here we are today making filters for just about any application on the market. If our filters did not work, we would not be in business growing every year.

K&N makes filters for Chrysler/Mopar, Ford Motorsports, Edelbrock, Rotax Engines, and Harley Davidson. K&N filters come as original equipment on the 2000 Ford Mustang Cobra-R. K&N even made filters for the Apache helicopters used in Desert Storm because of maintenance problems with the original paper design. If K&N filters work in these conditions they will work for you.

Thanks,

Rick Blum
Technical Support Supervisor, K&N Engineering
I still can clean my K&N filter another 30times compare to replacing the stock filter. as for the air flow....I think K&N still is better than stock. How I know??.....When you change it you feel the diff. in power band. 2cents worth. scx
www.knfilter.com web site, lists test data at 98% not 95%. y2kcorvette
And here I went assuming K&N is the way to go what with all the dust around here and being able to clean it out. Plus I read the bit about stuff flowing into the stock filter and gunking it up and figured this would be less of a concern with the K&N since I can just clean it out. I have K&N's in all my cages and they do well for them. I haven't looked at my original filter yet( I've only got about 2k on it), so maybe I should wait and take a peek at it before making any decisions. I just really like starting to collect all these little add-ons for when the weather gets too icky to ride much. Runaway #1259 (CO)
I won't try to repeat all the techie stuff on the different types of filtration materials. Mainly because I can't remember all of it. There are trade offs all the way around. You just pick your poison and live with it. I like the K&N for increased airflow at the risk of slightly higher pass through in some conditions. The oiled foam filters 'filter' more as they get dirty but do so then at the cost of air flow. Hard to have it both ways. K&N recommends that you not clean them too often. I clean mine with the oil changes. I also figured that eventually I would pay less for a reusable filter than for new OEM's which were $25 each (I think). The K&N is about $55 plus another $10 for some cleaner and oil. Brad, N. CA., 2001 F650GS - Inmate #1002
Suppliers for Motorcycles. http://www.knpowersports.com/
J. C. Whitney can special order K&N filters for you, but you need to call (and the right part number would probably help them). They got me one for my Toyota minivan (it really needed one). Marty #436-Chicago-97 F650F.
I just installed K&N's air filter on my 2001 F-650GS ..very tight fit! ... It's easer to install if one Loosens/removes the two big air plenum chamber screws, allowing the air box to move around a bit for proper alignments. I've done it both ways and I'd recommend loosening the air chamber. Any motorcycle shop can order filter for you with at the cost of about $50.00. The K&N air filter number for the F-650-GS is BM-6501. Carlcrom

Twin Air Opinions

At approx 3,000kms I switched to a 'Twin Air' air filter. I checked my air filter today at 6,500kms and the Twin Air snorkel side was 60% surface area coverred in dead moth bits and pieces of wings, bodies etc. The internal side of the Twin Air filter was perfectly clean. Fizz

F650GS OEM Filter

When I first took the air filter out under 10000ks of my 04 twin spark Dakar, I noticed that the soft rubbery base was damaged. The filter had to be replaced at the 10000k service. The filter is a very tight fit between the airbox and intake and this seems to be the problem. When I checked it recently it was damaged again so I decided to order a foam Unifilter. When I fitted it a few days later I took out the paper filter and noticed the base was badly damaged (letting in unfiltered air) and the paper element was also deformed. The Unifilter has a much more solid base and a much larger filter area and so far no problems. The airfilter on a H*nda XL250 is twice the size of the Dakar paper one. jutta
My original paper filter was deformed.. vent corragation channels were badly mis-shaped; the fit was tight, but not overly so that it worried me. Fizz
My filter is a tight fit and the act of sliding the snorkle over the rubber has damaged the seal in places. It helps if you use a small amount of silicone grease (available as Dow Corning DC-4 or available in any scuba shop) on the seal before you install it. My .02. Stick with the stock filter. It is way more efficient than the foam (holes large enough to through a cat through) filters. Here come the flames............... jetdocs550

Questions

When I get a New Foam Filter, do I need to Oil it?

Nope. If you got it from a Dealer in a Sealed Plastic Bag it is pre-oiled. Just use the Method Above to pry the plastic frame apart and reinsert it.
The foam does break down naturally after a while, sometimes lasts a couple of years, sometimes not. If you live in an area high in ozone, it will break down the foam fairly quickly. After 2 years some have noticed the filter starting to "dust", but a new pre oiled filter is only $6.

What is the Air box drain tube for?

The airbox gets gas, oil and sometimes condensation in it. If you oil your filter regularly there will be some dripping from that as well. Various bad conditions may have oil and gas flooding into the drain box, and thus the tube is there to drain it from the bottom. Normal airbox goo is a little water, some oil and a touch of gasoline from stopping your motor. So if your drain tap is busted, that stuff will just drip all over the bike instead of being routed into the tube.

How does the oil from an overfilled oil tank get into the airbox?

Via the crankcase.

What route does it take?

It drains down past the oil pump driveshaft into the crankcase. Then via the crankcase breather.

Under what circumstances does the oil actually get down the breather pipe/s into the airbox?

The oil tank breather runs into the cam cover. Then via the crankcase breather into the air box.
When the bike is stood for several days the oil drains down past the oil pump driveshaft into the crankcase. If there is too much oil it will submerge the balance shaft. There is the breather for the whole system that runs through the half hollow balance shaft . It runs from a 'window' at the back of the counter balance weight through the gallery in the generator cover then (small pipe near starter motor ) to the air box.
When the motor is fired up the oil covering the breather is forced up the pipe towards the airbox. In a few seconds the scavenge pump clears the oil back into the tank. That's why there is only a small amount of oil in the air box. There is a very low oil level in the tank when the bike has been stood and why it has to be run before checking the oil level.

How do I check if the breather is getting submerged.

When the bike has been stood for a week take off the breather from the generator case, fit on a length of clear hose put the other end in a jug and fire up the motor. No oil should get into the pipe.
I re-piped my Bimota to avoid the problem as the motor is inclined forward.
If you have an F650GS, a number of Riders have reported that after "laying it down" i.e. it fell over, they discovered a lot of Oil in the Airbox. See the GS Air Filter FAQ for more details.

Feedback:

After a recent long distance high speed trip, I found some oil in the airbox which concerned me. Took it to the dealer who did a compression test which proved all was OK. Apparently the crankcase breather which feeds into the airbox has a bit of a habit of blowing oil at high speeds. Dealer said that is why BMW put a drain in the airbox. Bit sceptical of that claim but hasn't been a problem since. Tink, F650GS Dakar, Brisbane, Australia.
Oil overfill question. What components need to be checked after it is diagnosed that the bike has been running over the oil level...and what are the short term and long term effects of running with too much oil in a GS? The only thing I would do is check the air box for oil and drain if necessary. The F650 engine is a dry sump design with a remote oil tank. The oil is pumped from the tank to the engine and overfilling the tank will have no impact on the lubrication system of the engine. It only takes as much oil as the pump will pump and the oil lines will flow. This assumes that the sump scavenge pump is doing its job and pumping the oil that drains to the bottom of the engine back to the oil tank. Overfilling the tank will only cause it to overflow, either into the airbox or on to the pavement. If the engine had a wet sump, the story might be different. Richard #230: 1997 Funduro.
I'm pretty sure I over-filled the oil in my CS. About 1/3 of my Airfilter is darker than the rest due to getting soaked with oil. There was also a bit of oil inside the airbox. I don't think it will really affect anything except emissions. I doubt I've been burning enough oil to damage the cat. wicked94pgt, BBG#22 F650CS, Natick, MA

How does Fuel get into the Airbox?

Normally there are two areas to look at and both are in the Carbs, for which you will need to refer to the following FAQs.

The Flat Valve O-Rings. See the Pukin' Petrol FAQ.
The Float Cut-off Valves. See the Carb Clean FAQ

Feedback:

Had a great ride last week from central AZ over to Santa Barbara...the bike (99 classic) ran great. Since getting home it has been having a tough time starting...really having to work the throttle to get it to fire. The bike sat for about 2 days, then this A.M. I go out and there is a puddle of fuel. Some has dripped out of one of the overflow tubes on the right side ( enough for there to be crystallization around the mouth of the tube) and then on the other side there is a steady drip. Fuel cock was on/ I usually don't turn it off unless it will be sitting for awhile. On the left side there is fuel moisture beside the Battery around the base of the air filter cover. Enough for there again to be crystals forming on the lower bolt. I pull the cover and fuel pours out. There is also signs of fuel on the carb area. Any help or ideas about where to go next would be appreciated. Paul #813
Sounds to me like the valve that is pushed up by your floats, to turn off the flow of gas into the carb float bowls, is defective and may need to be replaced. (Replacement of these valves is cheap and easy, but requires the removal of the carbs, which is time consuming and relatively difficult.) This is thoroughly covered in the FAQ, but in the meantime, turn off your fuel tap whenever the engine is not running.
I had exactly the same as this , it may be that you have some crap in the fuel system and the float valves are not seating properly you can just trying putting a lot of redex in the tank and giving it a good run, that might clear it out, if not its the carbs off I'm afraid which ain't the easiest of jobs, whilst you have them off you might as well check the jets, float levels and mixture screws as well. Alan BlackRat.
A little (or in the case of my Honda CB750, a lot of) oil and water will accumulate in the airbox from the engine breather, which is connected to the airbox due to emission concerns. The drain with the plug drains the airbox of this gunk (you have to pull the rubber plug to drain the airbox). There is also a tube connected to the fuel tank that will catch any fuel that is spilled around the filler cap. It is possible that you overfilled the tank and the tube was discharging the excess. If it continues, then you may have a leaky float valve. If this is the case, before taking the carbs apart again, try tapping the float bowls with a wrench and also try adding some chemical gas cleaner to the fuel. In the meantime, always turn the fuel tap off when stopping the bike. Richard #230: 1997 Funduro.
A small amount of fuel in the oil is normal, and gets burned off when the engine oil gets hot. A LARGE amount of gas will dilute the oil, lowering the viscosity so much it will not give a thick enough film of oil for protection (as Tom said, metal on metal). If the gasoline has filled your cylinder (the gasoline that trickles past the rings may be what's in your oil) and you try to crank it over, you WILL bend/break something, as the fuel (liquid) is incompressible. Usually the connecting rod is the weakest point and gets bent. First, fix the leak. Remove a spark plug (properly re-install it in the spark plug cap, and ground it to a good ground, to protect frying your ignition black box). Crank the engine over several times...since gasoline MAY come spraying out the open spark plug hole, best to do this outdoors, no open flames, stay out of the "line of fire" from the spark plug holes, wear goggles, have a fire extinguisher handy, (whatever precautions you deem appropriate...it ain't my place gonna burn down). At this point, drain the oil and change the filter (let it drain a good long time as it's viscosity will be high since it's cold - unless extremely fuel diluted). As Tom said, a second drain and fill may not hurt. Marty #436-Chicago-97 F650F

What are those 2 hoses on the Bottom of the Airbox?

by Dlearl#476 & Bob#550

Both of these hoses are BETWEEN the air filter and the carbs.

One hose is for any oil that gets in the air box, and it has the plug in the bottom to drain any oil. The parts list notes this as being "hose" and "plug", but doesn't say what it is really for.
The other hose is noted as being a "fuel hose". What is the purpose of that? It's a fuel tank vent.

Refer also the Canisterectomy FAQ.

Will an aftermarket filter improve performance?

It may result in a minor increase in performance. For examples see the GS Dyno Runs FAQ where there are examples of bikes before and after modifications.

Do I need to re-tune / re-jet my Classic F650 with a new UNI foam filter?

As the OEM filter is foam as well, I doubt if you'll have to do anything after replacing it with some UNI foam. dlearl

Are there any alternatives to air filter oil?

A google search reveals that there is actually a REASON for Air Filter oil being what it is...

"You can buy special air filter oil or use regular 30w engine oil. 90w gear oil also works good."
http://www.dansmc.com/aircleaner.htm

"Well designed filter oil :
Will spread on the filter evenly because it is fluid for the application.
Will repel water effectively, it wont turn grey
Will dry after a few minutes, and become tacky to the touch so it will trap dust better.
Will not be so expensive when compared to good 4 stroke oil, but then again from what you said, you may not be the type of fellow to buy top quality 4 stroke oil."

http://www.thumpertalk.com/forum/showflat.php/Cat/0/Number/680644/page/15/view/collapsed/sb/5/o/all/fpart/1

"Stick with the correct oil. There are two problems with using engine oil. Here's what will happen if you use engine oil on your air filter. It's not nearly as sticky as filter oil, so it will either get sucked straight through the filter into the engine, leaving your air filter unable to stop dirt and icky things from entering it, OR over time the oil will drip off of your filter, into the bottom of your air box, and utlimatley down to the floor of your garage, once again leaving your poor air filter to fend for it's self against dirt and other nasties. I prefer the non-spray types of oil, cause it seems to penetrate and coat the filter better. "

"I have been in this hobby for, oh let's just say a long time. Long enough to remember when there was no such thing as Air Filter oil and all we used was plain old motor oil. This stuff would dry out very quickly due to carburetor fogging, or just run into the airbox and leave the filter dry. It's not waterproof nor is it liquid enough to ensure adequate saturation of the filter. It isn't especially tacky either. IMO, Air Filter oil is a blessing. The other stuff will not last long, nor is it as effective. The new oils clean easily too. Look at it this way: You've got a high performance machine worth thousands of dollars. Does trying to avoid the small extra cost to protect that machine really make sense? To me it's pretty simple: Air Filter Oil is cheap. Top ends aren't. This ain't no lawn mower we're talkin' about here! The new 4-strokes are high performance, intricate machines. They demand much more maintenance and care, but will reward the rider with much more power and fun. Besides, for most of us, maintaining and wrenching on the beast is a labor of love - almost as much fun as riding it. We can all debate the intricacies of one air filter oil versus the others (No Toil, K&N, Maxima, whatever) but the fact remains the same: all of them, when properly applied, are better suited to the job than anything else."