CV carbs and pod filters

Thunderchild

Rumble, rumble.
If you're wanting to run pod type filters on a CV type carb, you know all the hassles of getting it jetted right all the way through the throttle range. I've done lots of forum searching on threads pertaining to the subject. Most everyone says keep the stock airbox.

Well, when I did my cb400T1 build I wanted to get rid of the stock airbox for purely aesthetic reasons. The huge airbox just didn't fit in with my visions of the bike.

This will work with the Uni type foam filters only. Not sure what you can do with the K&N type metal mesh filters...

The idea is to restrict the airflow back down to where it was with the stock airbox; keeping the air/fuel ratio the same as it was. Here's what I did...

I cut up some 16oz beer cans and made a round 'sleeve' to go inside the UNI foam filter. You can mess with the length to get the A/F ratio right. Just stick the aluminum sleeve inside the UNI pod filter and keep trimming the length until you get it right.

My first try, I was running way too rich -not enough air. I just kept trimming a little of the length off until it ran right.

I wasn't looking for a performance increase with the filters, and I didn't want to get into jetting the carbs. I mess with that enough on my dirt bikes. I just wanted a quick and dirty way to get the A/F mixture right. Some might call it 'ghetto', but it worked for me.
 
hell ya man! switched to pods to clean the look up to, massive airboxes are ridiculous. props to ya on the can idea! im messing with jets on mine right now. its not fun
 
Cool deal. I have a friend that tried the beer can restricters and it wasn't enough. We ended up putting in some PVC pipe couplings inside his UNI filters, along with the sleeves. Worked out great. I know it sounds ghetto, but it worked.

I know there's people out there that say the length and flow pattern matters along with the A/F ratio. I know that's true. But I'm just putting out there what's worked for me. I didn't have to mess with changing the jets or shimming the needle or anything.

The seat-of-the-pants dyno and plug chops says it works.

TC
 
very nice...so you just cut a piece of a beer/soda can and fitted it inside the cone filter? it's 3:21am. so i'm not sure i even read that right.
 
apreludem said:
very nice...so you just cut a piece of a beer/soda can and fitted it inside the cone filter? it's 3:21am. so i'm not sure i even read that right.

Cut the bottom and top off a can. Make a cut down the length of the can now. Roll it up and stick it in the filter. Trim the length of it if needed to fit the filter or to get the proper A/F mixture.

Like I said in the OP, you'll need a foam type UNI filter to try this.

UNI_Pod%20Filter%2003.jpg


Contrary to popular belief, any old can will work. ;)

TC
 
I believe the problem with running pods on CV carbs doesn't have to do so much with the amount of air and more to do with the way it's delivered. Stock air boxes utilize long intakes and the incoming air has an opportunity to be "smoothed" out, with less turbulence. Well designed and made velocity stacks will give you the same result without having to restrict air flow.
 
Sonreir said:
I believe the problem with running pods on CV carbs doesn't have to do so much with the amount of air and more to do with the way it's delivered. Stock air boxes utilize long intakes and the incoming air has an opportunity to be "smoothed" out, with less turbulence. Well designed and made velocity stacks will give you the same result without having to restrict air flow.

there's also something to be said about the carb bank pulling from a common air source. Something that can't be achieved using pods.
 
Sonreir said:
I believe the problem with running pods on CV carbs doesn't have to do so much with the amount of air and more to do with the way it's delivered. Stock air boxes utilize long intakes and the incoming air has an opportunity to be "smoothed" out, with less turbulence. Well designed and made velocity stacks will give you the same result without having to restrict air flow.

I think that is a big part of what the beer cans are doing..
I'd be wiling to bet that if the OP had blocked the outside of the filter to reduce the amount of air flow, it wouldn't have tuned as easily since the turbulent air would still be a problem. I think...

Anyway, I love the idea.
 
Sonreir said:
I believe the problem with running pods on CV carbs doesn't have to do so much with the amount of air and more to do with the way it's delivered. Stock air boxes utilize long intakes and the incoming air has an opportunity to be "smoothed" out, with less turbulence. Well designed and made velocity stacks will give you the same result without having to restrict air flow.

True. I alluded to this in a previous post. The point of me restricting the air flow is so that I could get the mixture where I needed without pulling the carbs to re-jet.

TC
 
flatcurve said:
there's also something to be said about the carb bank pulling from a common air source. Something that can't be achieved using pods.

True again. Having a common air source tends to smooth out the 'pulses' on the intake stroke.

TC
 
Thunderchild said:
True. I alluded to this in a previous post. The point of me restricting the air flow is so that I could get the mixture where I needed without pulling the carbs to re-jet.

TC

Word,
I'll likely be doing this on my next effort!
 
ejether said:
I think that is a big part of what the beer cans are doing..
I'd be wiling to bet that if the OP had blocked the outside of the filter to reduce the amount of air flow, it wouldn't have tuned as easily since the turbulent air would still be a problem. I think...

Anyway, I love the idea.

Yep. The air is drawn from the end of the pod filter, not from the sides. Like a velocity stack would provide. They have the added benefit of reducing the air flow to keep it from running too lean without re-jetting the carbs.

All my other bikes I went the conventional route of jetting, shimming or moving the clip on the needle, even playing with different tapers on the needle to get everything right.

I'm no stranger to motorcycle carbs. My CB400T1 was a quick & dirty build. I tried it as an experiment, and it worked for me. Just figured I'd throw the idea out there to see if anyone else wanted to try it.

TC
 
Sorry I posted this somewhere else already but I figured this is the best place...I found the site that sells them, what dimensions did you end up putting on your bike? Thanks man
 
Thunderchild said:
Yep. The air is drawn from the end of the pod filter, not from the sides. Like a velocity stack would provide. They have the added benefit of reducing the air flow to keep it from running too lean without re-jetting the carbs.

All my other bikes I went the conventional route of jetting, shimming or moving the clip on the needle, even playing with different tapers on the needle to get everything right.

I'm no stranger to motorcycle carbs. My CB400T1 was a quick & dirty build. I tried it as an experiment, and it worked for me. Just figured I'd throw the idea out there to see if anyone else wanted to try it.

TC
That all makes pretty good sense. I tore into my kz440 and took out the air box still waiting for some carb parts before it goes back together definitively going to try pods so ill be sure to try this first before messing with re jetting.
 
Interesting experience. If I understand you correctly, you basically have a straight thin wall tube inside the filter like a parallel wall velocity stack.

Parallel tubes with no flare on the end will reduce flow by around 5-10% according to people who have flow tested such things. The long straight section will indeed tend to straighten out air flow into the carb and the flow restriction caused by the parallel section drag and entry will change flow velocity through the carb.

I can rationalize why that might work, but I'd love to see a before and after on a dyno with A:F analysis to see what is actually happening.
 
It will also make longer intake manifold so probably 'better'
(oop's didn't check all the words came out)
 
Thunderchild said:
...

I know there's people out there that say the length and flow pattern matters along with the A/F ratio. I know that's true. But I'm just putting out there what's worked for me. I didn't have to mess with changing the jets or shimming the needle or anything.

The seat-of-the-pants dyno and plug chops says it works.

TC

Can I quote my own post? :) No chance to run it on a real dyno... At least not for me.
I know it's all unscientific...

TC
 
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