CV carbs and pod filters

I am actually trying this, got my UNI's and will be throwing them on my 440 build. I will post back here and inform others on how it works.

my friend has the super long UNI. filters on his CB350 Also running side covers, think he's got 110 jets but it runs well

Probably easier to get some radiator hose and mount filters further back.

hmm..sounds like a good idea, might try this on my honda with the wonderful cv carbs. From what I have read, the reason people say keep the stock airbox with these carbs isn't the airflow smoothness, its the amount of vacuum it creates...the more vacuum, the more the carbs open (this is what the cb-f people preach all day long on cb1100f.net). So with putting the restriction back into the uni filter, you create more vacuum...hence relieving the running problems. Like I said, I may have to try this

hope i'm correct in this info..

Dezmodromic said:

hmm..sounds like a good idea, might try this on my honda with the wonderful cv carbs. From what I have read, the reason people say keep the stock airbox with these carbs isn't the airflow smoothness, its the amount of vacuum it creates...the more vacuum, the more the carbs open (this is what the cb-f people preach all day long on cb1100f.net). So with putting the restriction back into the uni filter, you create more vacuum...hence relieving the running problems. Like I said, I may have to try this

hope i'm correct in this info..

Click to expand...

This is my understanding too. I'm interested in this greatly as I want to ditch the box on my '82 Hawk for aesthetic reasons too. I'll have to make the Keihin CV carbs work for a while until I can afford Mikunis. This seems like a solid temporary solution.

kj4130 said:

This is my understanding too. I'm interested in this greatly as I want to ditch the box on my '82 Hawk for aesthetic reasons too. I'll have to make the Keihin CV carbs work for a while until I can afford Mikunis. This seems like a solid temporary solution.

Click to expand...

I don't have the uni's (i've got the cone style) but I may tinker with this on those...if this is true, I should post this on the cb1100f forum and see how many panties I could ruffle...lol

The scooter guys do the same thing on their pod filters. But they use a sleeve on the outside. I think you can even get pod filters with an adjustable (sliding) external sleeve. The carbs on the scooters are similar Keihin CV carbs (PA or PB).

Slides in a CV carb rise because the air through the venturi is at a lower pressure than the air outside. As a motor runs faster the air through the carb goes faster and that drops the pressure and up goes the slide.

The low pressure above the diaphragm comes from the main body of the carb through a drilling into the bottom of the slide. Higher pressure (atmospheric) gets to the lower side of the diaphragm through a drilling on the intake side of the carb - usually a large slot.

Any "vacuum" on the intake side will effect both the air under and over the slide, so it shouldn't make a whole lot of difference. It will make a difference to fuel flow though and to air flow through the air jets. Unstable air will also cause the slide to move around when it should be steady. So it's better to have a large enough still air box (plenum) to smooth things out.

If you remove the airbox and fire up the bike you should be able to see the slides move up as you blip the throttle. If they "flutter" it's because of the reversion effect and an airbox helps to smooth that out too.

On a CB360 it's not possible AFAIK to get the carbs spot on just by changing fuel jets, the air jets need to change as well. That doesn't mean you can't make it run, but it will run better and cleaner with air correction jets or a stock airbox.

Teazer is right, you can't get 360 carbs 'right' with just fuel jet changes.
The slide 'flutter' is the reason SU carburetors on my Rover had oil filled 'dash pots' to damp slide movement
I'm pretty sure my 360 mods will work to 'fix' mid range on any Kei-Hin 3 jet CV carb?
It won't do anything for 'flutter' though as the only way to limit fas slide movement will restrict 'vacuum' through slide lift hole (although I'm working on something )

Uni filters work much better then the pods as a replacement of the stock airbox. The idea is to achieve the most stagnant air as possible. Plus the red colored uni filters look pretty cool. I run #105 jets on my cb350 and it comes out perfect.

Reviving this thread a little, as I've been researching this topic, online, today, a bit:
I think Thunder may be on to part of the equation. In a "ghetto" sort of way (his word, not mine.), he brought the factory restriction back AND straightened the airflow, so that now the air has to pass through the filter, change direction to the back of the filter housing, THEN do a 180 down the beer can sleeve, for a shot down the home stretch toward the carb. Many people online have mentioned how pods mess with the vacuum signal to the kidney-shaped post at the top of the CV carbs. Proper signal to this port is crucial to the vacuum slider's functionality, but it just may be that the Beer Can Trick solves this issue as well.
One of the jobs I've worked on involved utilization of a flow straightener that almost identical to this basic design. Only minor difference was the presence of numerous holes at the end of the tunnel where the air has to make that 180. They help in making the flow around the bend, easier. something that certainly can be incorporated into the beer can sleeve.
Obviously, if you are looking for HP payoffs, this MAY not be the method for you. BUT, if you are looking to streamline your bike, or just want that "cool pod" look (Don't ask me! I don't give a shit about image! ), this just may be the ticket.

bringin it back again....


any advice on how to determined if need to cut down the can?

also did u start out with the can fulling the full inaideof the filter any help would be great

Boy am I happy this thread was bumped.
This may be the solution I'm looking for!

Now to drink some beer...

rubber-side-down said:

bringin it back again....


any advice on how to determined if need to cut down the can?

also did u start out with the can fulling the full inaideof the filter any help would be great

Click to expand...

Yes, I started out with the can the full length of the pod filter. In an earlier post I mentioned that made it too rich. I trimmed a little at a time to get the A/F ratio where I needed it. After decades of jetting dirt bikes, I can pretty much tell using my 'butt dynamometer' where the mixture is. I would get it close then use plug chops to confirm it.

TC

Glad this has gotten revived. I had to lose my air box due to frame alterations and have been dwelling on the fact that getting the CV carbs to work correctly w/o the box will be tough. The box on my nighthawk was sealed except for a intake port on the top of the box. This leads me to believe that like someone mentione earlier that it's a stagnet air in the box. Kinda of like a restricted but large volume of air. I do remember years ago having a pair of kung fu slippers under my seat and the bike ran fine bottom and mid but had no top end at all. When I got home the shoes were jammed in the intake ports of the box. So I found out that it doesn't need alot of air coming in but a large volume to run correctly. Oh and the intake boots aren't straight from the box to the carbs either. Hopefully I can use the info here in this thread and some of what I just explained and figure it out. Any thoughts? I'll post some pic's of the air box when I get home, maybe that'll help too.

It's somewhat more complicated.
Air is constantly moving so never 'stagnant'
large volume slows down fast moving air from small intake

crazypj said:

Probably easier to get some radiator hose and mount filters further back.

Click to expand...

Tried that and totally worked for my bike! You can see the pics on my thread.

The air filter on my bike is no longer available so I was talking to an old mechanic the other day about changing to a foam filter and he pulled out his old set of carbs and they had inner tyre tubes around the pods to restrict the air,he said it worked a treat.

Just wanted to thank OP & say it worked for my gs450.
Bike was 100% stock a week ago, I removed airbox & had the foam filters lying around.
Threw them on & the bike ran ok like that for a couple hours then bogged.

Next day I got two 99 cent 16 oz energy drinks & went to work..
Cut them till they fit snug against the rubber inlet & the the foam backside,
which for my filters a 12oz can would have been fine.

BIKE RUNS AMAZING & HAS THAT JETTED FEELING & SOUND WITHOUT JETTING!
Its been about 2 weeks with no issues so far, guess it is just the right amount of air for my carbs.

JUST MY 2 CENTS MIGHT NOT WORK FOR EVERYONE BUT SAVED MY BROKE ASS.
THANKS AGAIN!

Glad to hear a positive report!
Like I said, it worked for me and it was a cheap, quick and easy way out at the time. It's rare that cheap, quick AND easy all work at the same time! 8)