Could this be the next "OIL"

[ribbert]

I have been doing some research about pod filters or uni-pods on CV carbs and many people say its just a bad idea.

Foam vs Paper

Nothing to do with CV carbs specifically.

The most expensive engines working in the harshest environments, earth moving and mining equipment, protect their engines with paper filters.
Long haul trucks, where every mile they can get out of a motor means money, use paper.
The most high performance cars in the world, Ferrari, Lamborghini, Porsche etc all use paper.
The fastest production bikes use paper.
Aeroplanes use paper.
Even you lawnmower uses paper.
The entire automotive industry with the exception of one model Ford (carbon impregnated dry foam lifetime filter) and the Fiat 500 (gauze) use paper.

YET.....

The net is overflowing with laboratory tests, scientific experiments, graphs, charts, YouTube evidence and testimonials providing irrefutable evidence that foam is better.

So it is no surprise that you will find people telling you it's a bad idea.

The answer ? ? ? ? ? ? ? ? ? ?

Noel

[VaughanCustoms]

Yeah I mean my Cougar has a K&N my Cobra has a K&N full intake so did my Ranger and my girlfriends Explorer and we love them. I really like the idea of not always having to replace my filter just clean and walk away. I guess pehaps I am just frustrated with my bike that I have a cotton media type filter on the bike and got a jet kit and got thrown for a loop. I have had this bike for a month now and she hasn't left the garage. My Cobra is able to get full use of the K&N because the computer has been tuned for extra air and full so I would assume it needs to be the same with the bike. Your tolerance levels on a motorcycle are definatly less than on a car running rich or lean in a car you will not really feel much performance difference but on a bike you can go from running to not running. I will have Randy tune up my carbs for me and I am sure it will fix the issues. Time to put it into a experts hands and as I learn more I will hopefully be able to return the favor in the future. I am working on getting a new job that I would work less hours and make more money so thats always good to not be on a huge money crunch all the time.

[jscgdunn]

I think the "bad idea" is because removing the air box and modifying the system needs a fair amount of experience to make it work correctly; which we have here.  The cv carb works great if it is set up right but a small change in velocity upsets the system. 

Pat ( I think he mentions it is his favorite subject) and others have explained this pretty well in the files section.  Added to the mix is that the is really very little increase in performance until you are in the very high RPM range....although the added intake noise sounds sweet to some!

As an example, we had an XS 400 with BS 34 carbs.  It would not start or run with the airbox cover off.  Put it on and it started and ran great. 

Many people new to bikes get into trouble (including myself) just doing what we did back in the day with cars.  No worky that way.

As everyone knows a carburetored car will run fine with the air cleaner off and it is (was) common to replace the stock air cleaner with a more simple system.  But those cars did not have CV carbs.

Some bike shops will not work on bikes that have the system altered.

Jeff

[Dads_FJ]

Just don't forget to oil your paper media filter, like the one in this old truck   It even tells you the oil level...

[FJ_Hooligan]

A few guesses:
Paper filters are probably cheaper to produce and thus cost the manufacturer less money. 
There is more money to be made by selling you a new filter every time vs. a one-time sell for a filter that you can clean and reuse.
Paper filters are very good filters, and they should be cheap unless you have to buy them from a m/c dealer.

I use foam filters because they are cheaper than the stock filter and I can maintain it myself.

Hooligan

[fintip]

 

[racerrad8]

...a one-time sell for a filter that you can clean and reuse.

Hooligan

Well, I know this supposed to be non-CV/FJ specific but why else would this discussion be had on the FJ forum, so here is the facts as I have witnessed over the years of working on FJ's, FJ powered race cars and building hundreds of carburetors.

There are three different media types commonly used for air filters:

Paper
Cotton Media
Foam

Paper is the O.E. filter of any form of manufacture; a single layer filtration media.

Cotton media is the highly touted "performance" K&N filter; a single layer cotton/oil filtration media. K&N used to advertise the gain of "(put a number here) by installing the filter. They have since been sued too may times for false advertising and they now claim, "Designed to Increase Horsepower and Acceleration".

Foam is usually "Open Cell" Polyurethane Foam; dual layer foam/oil filtration media in the FJ application.

Paper filters use a tight weave media that air must force its way through as it is cleaned of dirt. The paper filter is well documented to be the most restrictive.

Cotton media is a single layer media that requires the oil to be present for absorption of dirt particles and proper filtration.

Foam uses a dual density foam. The outer layer is a course open cell foam that is oiled on the outside to absorb the dirt particles and the inner layer is a finer density that is able to provide secondary filtering.

The issue of the FJ specifically is the camshaft timing resulting the valve overlap and the initial opening of the intake valve while still in the exhaust stroke. The millisecond of opening the intake valve prior to completion of the exhaust stroke of the piston results in backwash. When this happens the fuel in the carbs is exhausted out through the carb throat in a fine mist.

When the stock air box is installed the exhausted fuel mist is never in contact with anything but the boots inside the air box. So, paper, cotton or foam media types are not effected but the mist and all filter well.

When the air box is removed the filtration media is now placed at the throat of the carb opening. This then creates an issue with the fuel spray/mist coming into contact with the filtration media.

When this happens the fuel breaks down the paper type medias causing them to fall apart.

Cotton media filtration filter is usually a very course media which requires oil to filter. The fuel mist contacts the cotton media and washes away the oil. This then makes the filter about as effective a window screen over your carbs.

The dual density open cell polyurethane foam filter is able to absorb the fuel mist via the inner smaller density foam before it can reach the outer layer. The outer courser density foam stays oiled because the fuel mist cannot reach the oil and complete filtration is achieved.

The cotton media and foam filter are both a washable/serviceable filter that can be used for many years. The issue the becomes, do you want to be able to wash your filters in the sink or do you want the fuel mist to wash your filters and render them useless? If you have a K&N carb mount filter, take it off after you have some miles on it and see if the red oil is still at the bottom of the filter near the clamp. I find it usually is just light brown colored cotton media paper only.

I personally only use and recommend the UNI/RPM dual pod filter. They are usually half the cost of K&N filters and they do twice the filtering. I speak on this topic from an person with coming up on 20 years of FJ experience building engines, carbs and racing & riding them for years.

If you want the best air filter for you FJ buy the dual foam filter. Is addresses the specific issue of camshaft overlap & fuel misting while still maintain the oil for effective filtering.

If you don't believe me, take off your filters or air box. Warm up the engine and crank on the throttle a few times while looking down at the carb throats, you will see the fuel spray out of each carb. Heck hold you hand pretty close the carb and crank the throttle, you will see just how wet your hand gets. Now imagine that spray coming out of every other stroke of the 4cycle engine. So at 5000 rpms the fuel mist comes out of each carb 2500 time per minute.

That is a lot of fuel spray and you need a filter that can handle the absorption issue and the K&N "one-time sell" filter is not the best thing for your engine as you don't get a chance to wash it yourself, the engine does it for you.

RPM Dual Pod Foam Air Filter

Randy - RPM

[The General]

I wuv you Randy!

[fintip]

Why does the fuel not break down the oil when it is suspended in foam, but does when it is suspended in cotton? Is the theory that it doesn't get past the finer inner layer, but the oil is on the outer layer?

Thanks for that post, Randy, that was great. Adding it to the wiki. 

Still messy, but lots of data there to be organized later:

http://fjowners.wikidot.com/pods

[racerrad8]

Why does the fuel not break down the oil when it is suspended in foam, but does when it is suspended in cotton? Is the theory that it doesn't get past the finer inner layer, but the oil is on the outer layer?

Not theory...experience.

It is not so much as it "breaks it down", but dilutes it and allows it to be ingested into the engine as it is too thin to stay in the filter.

Yes, the cotton media filters are a single layer and require the oil to filter.

The foam is a dual layer approximately .620-.750" or 5/8-3/4" of an inch thick.

It has been a long time since I cut apart a K&N filter, but I believe the cotton media was about .020-.025" or 1/50 of an inch thick.

Another test is to hold a cotton media filter up to the direct sunlight and see how big the sun is through the media. When you hold up a dual density foam filter is almost looks like a kaleidoscope because the sun is being diverted from direct through the media and must change directions of the dual density media.

Randy - RPM

[aviationfred]

I had a severe fuel leak over the weekend and removed the stock airbox and carbs to investigate. Found a stuck float. Got everything cleaned and put back together. Getting the airbox and (for the loss of a better term) stock velocity stacks back on was an endeavor that I NEVER want to experience again. Thank You Randy for your input on this subject. I just ordered a set of the Uni duel pods.

Anyone need a used Uni stock foam air filter?

Fred

[fintip]

Fred, I could use it. I'll convert eventually, but not yet, and I do need an air filter.

[X-Ray]

RPM Dual Pod Foam Air Filter
Randy - RPM

Will be ordering a set very soon. We all wuv you Randy, 

[RichBaker]

I have been doing some research about pod filters or uni-pods on CV carbs and many people say its just a bad idea.

Foam vs Paper

Nothing to do with CV carbs specifically.

The most expensive engines working in the harshest environments, earth moving and mining equipment, protect their engines with paper filters.
Long haul trucks, where every mile they can get out of a motor means money, use paper.
The most high performance cars in the world, Ferrari, Lamborghini, Porsche etc all use paper.
The fastest production bikes use paper.
Aeroplanes use paper.
Even you lawnmower uses paper.
The entire automotive industry with the exception of one model Ford (carbon impregnated dry foam lifetime filter) and the Fiat 500 (gauze) use paper.

YET.....

The net is overflowing with laboratory tests, scientific experiments, graphs, charts, YouTube evidence and testimonials providing irrefutable evidence that foam is better.

So it is no surprise that you will find people telling you it's a bad idea.

The answer ? ? ? ? ? ? ? ? ? ?

Noel

Every lawn mower I've ever used hasn oiled-foam filter....  Otherwise, dead on.

[RichBaker]

Just don't forget to oil your paper media filter, like the one in this old truck   It even tells you the oil level...

I had a '51 F-1 in highschool, had that very filter on it....  Loved that old truck!