Pod Filters?

I have seen a couple of XJs with pod filters on the carbs... I am going to have to install them (I may or may not have cut my airbox in half) and wanted to see what people thought of them. What should I expect performance wise, I know they will be much louder.... I will jet the carbs, but is there anything else I should do when installing them? Thanks for the help

 

what exactly are "pod filters" and can any one post a pic?

 

I am at the bar right now, but when I get home I will post a link to the forum with the pic

 

Nothing will be louder.

 

I am running straight pipes x4, I hope my exhaust is louder than the intake... Will I be disappointed??

 

You won't hear anything different with pod filters. And with straight pipes you won't really hear anything else at all. I hope you like it loud. Me personally, I love it. But I'm going to wind up having to run mufflers because my job moved over the state line to missouri and I have to have mufflers now. Damn state legislature.

 

My friend ran into the "muffler" issue in the city of Ottomwa (sp), luckily his pipes were long enough that they were considered legal... I am pretty sure mine won't be legal in a few areas, but that is 1/2 the fun (until I have to pay the ticket).

 

Flash, in this post you can see the pod filters off the carbs... it is the 3rd picture down.

http://xjbikes.com/Forums/viewtopic/t=28706.html

They do look great

 

thanks Scizor but what are they for?

 

They replace the air box located under the seat. They provide the intake to the carbs. From what I have read and heard, the usually provide quite a bit more airflow... Since I have cut my air box in half, they are about my only option for filtering the intake air (although I was originally going to make a new air box out of a WWII ammo box, but decided the pod filters would be easier/more efficient).

My main concern, which has been verified, is that they will produce considerably more noise since there is nothing to quiet the air flow, which the air box was pretty good at.

If you want a quick example, start up your car and take the cover off your air filter and you will here the intake growl.

I just hope the growl isn't too bad. Hopefully there will be a performance increase as well.

 

SovereignDragon

When I was changing to a 4 into 1 aftermarket exhaust, I decided to just run the bike with the 4 stock down pipes... I think it made my ears bleed, but I loved it. My goal is to have the custom exhaust just as loud, I just have to pray I don't move to a state with vehicle noise regulations which are regularly enforced!

 

god, i hate overly loud bikes and cars. They're the reason for the laws. If everyone just ran some pipes that were somewhat acceptable, there wouldnt be an issue, and it wouldnt ruin it for the rest of us.

 

You do have a point vanimal... when discussing the issue of loud bikes, my group of riders (all Harley save for me) and I can't help but laugh at how true the South Park episode about Harley riders it (if you haven't watched it, please do. I guarantee you will get a kick out of it).

While I have run my bike with just the 4 down pipes which were ridiculously loud, that isn't the sound I am going for. My only point was that I hope my exhaust is louder than my carb intake. I will say that I do notice that car drivers are more aware, and subsequently more cautious, of me when I am only my bike with loud pipes than when I am on my quiet bike.

Just my opinion

 

Pod filters are a tuning nightmare, be prepared to spend lots of time removing and reinstalling them to change jets. The CV carbs on XJ's don't like having the extra airflow. While it may be possible to make one with pods run as well as one with the factory airbox, I have not seen one. All the XJ's I've seen with pods don't have good throttle response and run lean, even after re-jetting. The bikes you see with pods and run good usually have smooth bore carbs and not the CV carbs. While pod filter look really cool they are a pain to tune and will give you a minimal power increase. If you are looking for power, install a 4 to 1 exhaust and a K&N style high flow filter in the stock airbox.If you decide to go with pod filters keep the airbox intact, you may want to reinstall it someday or sell it to someone else who does not want pods.

 

mlew, I wish you would have posted that before I cut my airbox in half. Since I am at the point of no return, I will ask perhaps a stupid question = what is a "smooth bore carb" vs. a " CV carb."

At this point I haven't sunk much money into my bobber rebuild so spending the money to make sure I do things right is very important.

Thanks for your input!

 

CV (consant velocity) uses the rubber diaphram on top the carb to meter fuel flow depending on airflow. The carb slide provides a little air restriction to draw fuel in the airstream.
Smooth bore carbs use a venturi to draw fuel, no diaphram and slide. The faster the airflow the more fuel is drawn. Just like most older auto carbs.
Thats the simple basic explanation.

 

Okay, I understand the basics (and I thank you very much). I have to ask another beginner question, I am sorry... Am I able to convert my stock carbs, or am I stuck purchasing new ones?

Can't thank you enough for your help... my first bike project has been so much fun so far, but I have so many questions it is crazy. Everyone on this site has been so much help. I can't believe how willing people are to lend a helping hand

 

Can't convert carbs from one style to another. People have fitted other carbs on their XJs. I think some older Suzukis and Kawasakis had smoothbore carbs that can be installed with a little work. Do a search on this site for pod filters, there are several great articles on tuning for pods.
Aks any question you need, there will be someone here that can help. I've been in the garage all day working on a XJ1100 project and its nice to take a break and spread some knowledge.

 

You should use the search function on this site. You can get a lot of opinions, and tips, also some dreadful horrible accounts from those who have failed. Failure is not however certain, with patience and the ability to learn from mistakes. And you need to own a screwdriver, and know how to use it.

 

Just be gutsy and make the giant leap to EFI!!!
Finding a rack of smooth bore carbs will be a lot more difficult and expensive than buying a used airbox off Ebay and going back to stock intake.

 

Not sure how many people get that reference, but I do. Hilarious.


Also changing to pods does not make the bike louder, and certainly not enough to drown out exhaust noise. I understand what you refer to when you used removing a car aircleaner as an example.

 

The real question is why? I've read many dyno tests on motorcycles and usually they respond better to exhaust tuning than tinkering with the carbs or cams with the stock redline. My 750 has 33 mm valves and 32 mm carbs, the valve stem diameter and other restrictions in the air flow like the curvature of the ports and the valve head also play a part. The carburator venturi works by having a greater restriction between the atmosphere and the cylinder than the the port & valve. If the carburator is less restrictive than the valve & port, vacum will become zero and the airflow will reduce and the bike will slow down or sneeze back through the carbs. The factory airbox work pretty good, just the snorkel and filter element are too restrictive, you'll get more, even, flow by opening up the air inlet to the box and putting a K&N filter inside it. I went farther, it came with a price the 3000-6000 rpm acceleration faded after jetting it rich enough to stop the backrapp (no mufflers) and the mileage decreased as well. Most guys I've talked after switching to pods, never got their bikes to run right. A good set of headers (open or closed) and a k&n filter with the right jets would most likely yield as much or more horsepower and torque than anything else with stock heads, valves, cams, etc. If not I'd suggest getting a bigger engine (or a much lighter bike frame lol)

 

To answer the "why question," looks. With relocating the battery most of the wiring to a box mounted on the rear wheel, I wanted there to be nothing under the seat. Removal of the air box and the installation of pod filters was key to the look. Unfortunately, a bike that looks good but runs like crap isn't of much use to me.

There was a post about going all out and changing to EFI, this is probably a very dumb question, but here goes. Is that actually possible? My 2009 VStar is EFI and I do love that bike... although it loads up because they forgot to tell me that the Cobra pipes I put on did not have an O2 sensor so the computer has no clue how to burn the fuel every once in awhile (looks like I am taking the O2 sensor out of the stock pipes and drilling them into the Cobras this winter as well as working on the XJ).

Thanks for answering my really dumb question.

 

You can get the bike to run fine. Those who say otherwise have probably not tried. It may or may not suffer a minute amount of power on the dyno, but garunteed not enough to notice in the real world. I have 2 bikes excactly the same model year size. One with pods one factory. They both perfom the same throughout the entire power band. It just takes an ability to learn. The main thing I found was adding the stock airbox velocity stacks to the pods. Other than that, jet up, do some shimming, color tune and test ride, repeat. I had it dialed in on one afternoon.

 

MAIN FUEL JET SIZE CHANGES NEEDED PER TYPICAL MODIFICATION:


Typical Exhaust Changes:

+2 main fuel jet size for custom 4-into-2 exhaust

or

+4 main fuel jet sizes for 4-into-1 exhaust

or

+4 main jet sizes for no muffler (open headers)


Typical Intake Changes:

+2 main fuel jet sizes for single K&N filter (inside a stock airbox)

or

+2 main fuel jet size for drilling holes in the airbox with stock filter

or

+4 main fuel jet sizes for individual pod filters (no airbox)


Additional changes:

- Add up all the main fuel jet size increases and subtract 2 sizes.

- Decrease main fuel jet size by 2 sizes per every 2000' above sea level.

- Under a mis-match condition, such as when using pod filters with a 100% stock exhaust, or 4-into-1 header with stock filter and air box, then subtract 2 main fuel jet sizes.



PILOT FUEL JET SIZES CHANGES NEEDED PER TYPICAL MODIFICATION:

Pilot fuel jet size changes are related only to the change in main fuel jet sizes according to the main fuel jet size formula described above. Note that this pilot fuel jet rule is for the main fuel jet size change BEFORE any main fuel jet altitude compensation is factored in:

Increase the pilot fuel jet size +1 for every +3 main fuel jet size increases.

Additional changes:

- Decrease pilot fuel jet size by 1 for every 6000' above sea level. This should be a good place to start. You use the pointie end of the screwdiver right.

 

bobberaha: Thank you! That was a ton of help... Thank you very much!

 

This should give you an ideal of where to start just remember to use the pointie end of the screwdriver.

 

I have to ask this question... There have been many references to the correct way to use a screwdriver, what are you all talking about? I feel like the kid in middle school sitting alone at the lunch table on this one!

 

If you click on the xjforever on top of the screen and go to the information overload hour and scroll down to the carb section there is alot more info on jetting from Chacal.

 

Thanks, there is so much information on this site it is often hard to find exactly what I am looking for... much appreciated.

 

What do the velocity stacks do? I have pods on mine. Has a rough spot right at 5000-5500 rpm. No clue why.

 

Velocity stacks effectively lengthen the total intake track ( from filter to intake valve) which increases the weight of this air and the dynamics of how the cylinder would be filled, possibly moving a torque curve and hopefully raising peak HP.

It also gives a little headroom, because carbs spit gas back upstream when the flow reverses, and they also straighten and shape the airflow, and impress your friends that don't have them.

 

Well impressing my friends was not really in my mind when searching to clear up the flat spot through my rev range. If you have the stock airbox boots throw them on the pods and try it. Please tell me if it doesn't help and I will shut up about it.

Link in my signature of reference to boot size.

 

TimetoRide that is what Streetbrawler has done by putting the stock airbox boots on the pods he increased the length of the boots back to stock length. It gave the air time to stream just like it does coming out of the stock air box only at a higher volume.that is why he was able to tune his bike to run through all ranges of throttle. the short boots on the pods are what causes the turbulance the air does not have time to stream. there is another post where a tube was inserted into the center of the pod still using the pod boots. yes he did restrict the airflow but more importantly he increased the length of the intake tube giving the air room to stream.

 

where did this myth come from about airbox airflow being smooth and pods having turbulence?

not for the xj but on my suzuki i made a "wind tunnel" type of thing where i cut 3 different intakes in half including the filters and mated them to a piece of glass. i used a fine tip on a bee hive smoker and watched the air stream coming through the filter and down the tract. the airbox, similar in design to that of an xj, was the worst, the intake air eddies around after the sharp cornered exit from the box, with no bell to smooth things out.

as for the clamp on filters, they were smooth as a babies behind.

 

awesome zookie, way to shut 'em up

 

I'm sure you realize that the airflow only "flows" a little more than 25% of the time due to valve timing - - that the airflow is more like a jackhammer than a garden hose, and that smoke tests and shop vac tests are never going to display the true characteristics.

Considering this, would any vortex continue to spin when the air stops and reverses, or would the turbulence itself need to also reverse, or , would the reversal create NEW turbulence on the lee side of any obstructions ??

I would agree that longer, straighter, smoother runners are better.

 

Yes anything that impedes or changes the direction of airflow will cause turbulence. By adding pod filters with longer intake runners you reduce the reversal in flow due to the fact you are not pulling air from a common source. I.E a stock airbox has a common plenum when intake valve #1 is open and pulling in air it is pulling it from the common area therefore it will reverse the air flow from all other intakes in that plenum causing turbulence. I will agree that installing pod filters on our bikes is a huge pain in the ass but if you are willing to put the effort and time in it takes to jet and tune to the pods there is no reason these bike cant run as good if not better than the stock set up.

 

^ what he said.

 

i thought of the exact same problem when i built the makeshift wind tunnel, so instead of a shop vac i used an air compressor intake (coincidentally close in displacement to my suzuki) to suck the air through and as a bonus i could vary the rpms because its gas powered with adjustable throttle.

admittedly, the reversion, valve opening, and max rpms are nothing like the real engine, but certainly gave a better example than a solid flow.

what i saw with the minimal reversion the compressor had, was that any vorex would actually "back up" with any real amount of reversion. it was minimal and again, my test was nothing like the real thing when it comes to the true pulses and reversion of a cam/valve engine.

my test was aimed more at watching the velocity of the intake charge and to check for any turbulence, and i used the stock airbox just for "control". as a side observation, i can say that pod filters do NOT create turbulence.


FWIW- it was very easy to build the quasi-wind tunnel, anybody with spare time should try it out, its pretty cool.

 

You guys have all climbed way out on the wrong branch of the tree.

It's not about turbulence; it's about finite vs. infinite air supply and its effect on VELOCITY.

CV carbs=constant VELOCITY. The reason that putting the airbox boots back on works is because they perform the same function as...

VELOCITY STACKS. There's a reason they call them that. Racers don't run wide-open carbs, they run velocity stacks. For a reason; even on non-CV carbs.

Debate the how all you want; the science is all about air velocity. And smoothing out any inherent turbulence probably does help increase velocity.

 

Thanks fitz, all I really know for SURE about carburators and tuning is that putting the boots on my pods helped me. I know that for a fact. Otherwise, I am still learning from ALL that is posted on this website.

 

Whether you call it "turbulence" or not, the simple fact is (as pointed out in MANY other threads) that pod filters alone do not shape the air charge coming in to the intake horn on the carburetor. Also, as a result of basic fluid dynamics, air being pulled from an infinite source (see above post about the common atmosphere in the stock airbox) has a tendency to vortex. It also enters the carburetor at a reduced velocity, which is critical to getting the CV slide to operate properly. The oval shaped orifice on the top of the carb intake horn supplies the air necessary to lift the CV slide, allowing the proper amount of air and fuel to enter the venturi through the emulsion tube. This oval shaped opening requires a positive pressure atmosphere to function properly, which is supplied by the shaped air charge coming through the velocity stacks or through the stock airbox boots. The vortex air stream created by pods, while not technically turbulent, inevitably produces a negative pressure atmosphere behind the CV slide air opening, which in turn reduces the proper function of the slide, which results in a nearly impossible to correct ultra-lean condition. In short, pods can be used, but if you want to protect your engine then there MUST be some sort of tube between the pods and the carbs to provide a shaped, high-velocity charge of air to the carbs. After over a year of trying to dial in with only pod filters (for some reason there isn't room on my bike for velocity stacks) I have ordered a stock airbox to reinstall on the bike. Just my $0.02

 

im not really interested in debating the pods vs airbox anymore, i was just tired of seeing "pods create turbulence" posted everywhere. important to the debate or not, that myth needs to die.

 

swguy270.

The Oval Orifice at the Top of the Intake Horn is an Atmospheric VENT.
That VENT is the sole supply of AIR to:
>>The Pilot AIR Jet
++The ==> MAIN <== AIR Jet.

The Lowering of Pressure at the VENT Opening robs the Main AIR Jet of the supply of AIR needed to surround the EMULSION Tube.

Without that AIR supplied to surround the Emulsion Tube and be drawn-up into the Intake Air with (and) atomizing the Fuel.

The Carb just don't work right.
Cant.
Needs air.

 

Ok so I had the dynamics backward. Thanks for the clarification, Rick. So the orifice provides air to the pilot and main air jets and does not provide the pressure necessary to raise the piston. I must be dyslexic. i am apparently understanding things backward. Thanks again. I had for some reason formed the idea that the lack of airflow through the emulsion tube was a result of the slide not receiving the proper vacuum signal. BTW just so everyone knows, I have absolutely NO problem being corrected when I make such a mistake. Please do, in fact. This is how we learn.

 

You had it right.
Your explanation of the lowering of pressure at the Orifice Opening was the Critical part of the deal.

Additionally, the lowering of pressure at the Orifice reduces pressure within the Atmospheric Chamber BELOW the Rubber Diaphragm.
>>Making it more difficult for the Diaphragm to collapse, ... causing the Piston to NOT rise as efficiently as it should.

Until recently, ... the only way to deal with the LEAN Condition resulting from Pods was Shims and Re-Jetting.

Now, understanding that the Intake Horn of the Carb NEEDS a Shaped and Accelerated Volume of AIR at the Intake:
> Experimentation on Manifolds and Internal Velocity Stacks has been initiated by Forum Members.

We've done more to solve the Pod Dilemma in the past 18-Months than all the Shim and Jetting Sites have done in over 25-Years.

Personally, I think the "Orifice Bypass" I conjured-up, by blowing smoke rings at a Carb hooked-up to a small Shop vac, ... will help solve both the LEAN and POWER BAND Issues, in short order ... once someone tries affixing a Cover Plate to the Atmosphere Orifice and Drilling a Bypass Hole atop the Intake Horn.


(PHOTO: Mikuni Intake Horns. Hitachi Carbs similar.)

 

Has anyone heard of taking the bike to a Dyno and have it professionally tuned? I mean if you are banging your head against the wall trying to tune it yourself, why put yourself through the aggravation?

 

Cause we're modders here Taking it to a Dyno would take all the fun out of DIY.
Just IMO
I'm interested to see how the drilling and orfice blocking will work! Be nice to have another set of carbs
-Chris

 

I'm looking forward to hearing the results of someone who modifies their Carbs with the "RickCoMatic Bypass".

I feel certain that a large percentage of the Lean Condition will be improved upon, once some AIR is presented to the AIR Jets to improve the quantity of Fuel drawn-into the Engine via the Main Jet through the Emulsion Tube.

I think the Diaphragm Piston will lift better and Main Jet Fuel will be supplied in a manner closer to Normal than without the Bypass when outfitted with Pods.