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Discussion Starter · #1 ·
So with the increasing number of CX'ers putting pod filters on their bikes (myself included), I'm wondering if anyone has thought of a combination pod filter / velocity stack.



One of the gripes of having pod filters is that it allows for side drafts (or rather for air to come in at all directions) which can have a significant negative impact on overall performance. Simply put, the stock airbox has the upper hand vs. pod filters because of the way it channels air evenly and directly into CV carbs (with no turbulent airflow)



However, I'm wondering what kind of performance would be gained by inserting a velocity stack inside the pod filter. I imagine this would decrease the amount of side draft, and increase the amount of "straight-line" air coming into the carburetor. Would this be one way of replicating the stock airbox?



I'm planning on picking up some plastic/rubber or metal tubing that will extend approximately 3/4 of the way into the pod filter.



They seem to have kits available for Ducati Monsters:

 

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I like this idea as well. It may be a good solution, long term, for the cracked/split boot between the carburetors and the airbox. Plus, I have always liked the looks of a pod filter. I just never went with them because of the work involved with modifying the jetting.
 

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Discussion Starter · #4 ·
I'll have to find something that has a 54mm (approx. 2 1/8in) inside diameter. I'm thinking that exhaust tubing will suffice since it's also thin enough to sandwich between the pod filter and carburetor. They have the kind that start at one diameter and end at a larger diameter. With that kind of tubing, I can replicate the curved lip seen on other velocity stacks. I'll just have to cut it to length and pop it in! This might be easier than I thought!!!



This is what I'm looking for (any parts store should have it).

 

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NO DO NOT, I HAVE THEM ON MINE. You have to plug them up with a sponge or tape because it makes the carburetor lose vacuum from to much airflow which messes your carb up like a biattcchh thats what im dealing with right now trying to adjust it. Check out my bike you can see them
 

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NO DO NOT, I HAVE THEM ON MINE. You have to plug them up with a sponge or tape because it makes the carburetor lose vacuum from to much airflow which messes your carb up like a biattcchh thats what im dealing with right now trying to adjust it. Check out my bike you can see them


Please explain, calmly and clearly, what you mean. Do you mean that you have the pods? Do you mean that you have the pods and the velocity stacks? We are interested in using both the pods and a velocity stack. We already know that the pods create issues - that is what we are trying to correct.
 

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I have to tape mine completely up to have it run any good at all, you can put them in for looks but shove a dense foam or spong in it

Ive tried the stack didnt work to well
 

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I have to tape mine completely up to have it run any good at all, you can put them in for looks but shove a dense foam or spong in it

Ive tried the stack didnt work to well


You had to tape what - the pods or the velocity stacks? Both?

Shove a dense foam or sponge into what - the pods or the velocity stacks? Both?

When you tried the stack that didn't work well, did you try it by itself or with the pods?

What type of velocity stack were you using?

What types of pods were you using?



You obviously have experience, but we cannot read your mind or see your bike. Please slow down a little and be a bit more clear. I am very interested in your bike and what you have tried. I hope to learn something from you, but the way you post your answers and questions is very confusing.
 

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You had to tape what - the pods or the velocity stacks? Both?

Shove a dense foam or sponge into what - the pods or the velocity stacks? Both?

When you tried the stack that didn't work well, did you try it by itself or with the pods?

What type of velocity stack were you using?

What types of pods were you using?



You obviously have experience, but we cannot read your mind or see your bike. Please slow down a little and be a bit more clear. I am very interested in your bike and what you have tried. I hope to learn something from you, but the way you post your answers and questions is very confusing.


My pods i had to tape

I tried with both, it bogged down when i went on the throttle and had rough idle

K&N i believe?

Custom made aluminum pods from a machine shop



This was of course while it was running, i bought it it didnt have the original airbox so i tried these 2, the pods with a dense sponge inside of it to block air seem sto work better.



and im very tired construction jobs take a toll on your mental haha
 

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My pods i had to tape
This was with just the pods?

I tried with both, it bogged down when i went on the throttle and had rough idle
This was with both the K&N pods and the custom aluminum pods? How did you manage to get 4 air pods, mismatched, onto two carburetors?

K&N i believe?
This makes sense - I am familiar with K&N filter products and I know that they make very popular pod filters.
 

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Custom made aluminum pods from a machine shop
This is where you lose me. Are you talking about custom made aluminum air pods? If so, what type of filtration was used, if any. Or, as I believe you meant to say, you were also using some custom made aluminum velocity stacks. If this is what you meant, did they go between the pod filters and the carburetor? Did they extend into the pod filter? Are you sure they were velocity stacks and not just mounting adapters for the pod filters?



This was of course while it was running, i bought it it didnt have the original airbox so i tried these 2, the pods with a dense sponge inside of it to block air seem sto work better.
This makes sense. Were you using a washable filter? They pass more air, so maybe a good disposeable pod filter with finer filtration and less air flow may help without having to use the sponge.



and im very tired construction jobs take a toll on your mental haha
This makes perfect sense - get some good food and some sleep.
 

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Discussion Starter · #14 ·
1978CafeRacer...I guess I'm still just a bit confused as to exactly what setup you had.



Just a bit more background on my own setup:

Carbs rebuilt by Larry with 90/120 jets

K&N Air Filter (Pods)

MAC 2-1 Exhaust with EMGO Shorty muffler

Fresh Spark Plugs and new coils



My plan is this (as best I could with Paint):

The black is the outline of the Air Filter (Pod)

The red is the Velocity Stack inserted into the Air Filter

The blue shows the flow of air into the Air Filter and then redirected around then into the Velocity Stack







1978CafeRacer...Is this something that you have done before? Thanks
 

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LFE concept
1978CafeRacer...I guess I'm still just a bit confused as to exactly what setup you had.



Just a bit more background on my own setup:

Carbs rebuilt by Larry with 90/120 jets

K&N Air Filter (Pods)

MAC 2-1 Exhaust with EMGO Shorty muffler

Fresh Spark Plugs and new coils



My plan is this (as best I could with Paint):

The black is the outline of the Air Filter (Pod)

The red is the Velocity Stack inserted into the Air Filter

The blue shows the flow of air into the Air Filter and then redirected around then into the Velocity Stack







1978CafeRacer...Is this something that you have done before? Thanks


I like your idea, and I think it could be used in conjunction with a flow element similar to those found in a Mass Air-flow Sensor...and LFE or Laminar Flow element which would basically be, simply put, a bunch of soda straws gathered together in a bundle.



http://www.tetratec.de/lfewie.html
 

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I have also thought about doing the internal velosity stacks with individual air filters on the outside of the stacks and carbs. I'm running TM-38 flat slides and I don't have the vacuum problem just jetting problems ha ha. Runs strong though.

Cheers, 50gary
 

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he started out with velocity stacks and could not get the bike to run right and has no gone to pods is what i believ he was trying to say
 

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I'm wondering if this would smooth out the airflow at all. I'm thinking you would at least need a bell. I read a technical document on the difference the bell shape and length make on the aerodynamics of incoming air - way techy and pretty complicated. It seems CV carbs will simply never perform at 100% with pods, every old school mechanic I talk to in town tells me they're a bad idea. Sure they work ok, but I don't think we'll be winning any races. You probably need to get some flat or round slides to get the performance gain and efficiency you're looking for. Then you can begin the mindfuck of jetting from scratch with pods and free flowing exhaust... These projects never end do they, haha.
 

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Remember that changing exhausts affects tuning as well.The Mac 2 into 1 exhausts are not as well designed as the Motad 2 into 1 exhausts.The Motad 2 into 1 are fire and forget on a standard CX e.g no requirement for re-jetting.They work out-of-the-box.

I will freely admit I don't do any of these modifications(I have run a Motad 2 into 1 and they are great but was too quiet for me but did seem to add power) but with my knowledge of these engines/systems I'll proffer this for thought,



1:On a stock machine if you fit a Mac 2 into 1 e.g remove the collector box and proper tuned exhausts you have to re-jet.



2:If you remove the Airbox system which alters the Constant velocity partial vacuum at the Carb intakes you have to re-jet.



That's a,"Double" re-jet/whammy or tweaking IMHO to get the engine back close to it's optimal power-band.



IMHO the best option would be to ditch the Keihin carbs and go for a more linear set of older style,"Slide" carbs.



These will most likely not give the best economy but should give the best power performance.The original system was designed to be fuel efficient but if you don't care about mpg and want power see above.If I were going to do any of these,"Power" mods I'd ask JimL nicely for information as with out a doubt anyone who can get a CX500 over 140 miles an hour must be an absolute expert on carburetion.





My 2 cents.
 
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