CV carbs and pod filters

I chuckle when people put LARGER carburetors on, ostensibly for better flow, then put TINY pods on, which flow much less than stock airboxes....

If you understand volumetric efficiency at all, you can understand why those small pods are more restrictive than either stock, or larger type pods.....

D4N63R said:

is the secret mikuni's? hahaha

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Joon-yah Bourelle said:

nope, I run the factory cv carbs!!

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CB/CM 450 uses 2 jet not 3 jet so can be modified reasonable easy
Mikuni VM are not a solution if they are too big plus come with the wrong parts inside.
Just about all need re-jetting, most need new slides and proper emulsion tubes fitted even when they are the correct size for motor

I saw this CB250 Bobber at a local show late last year which gave me the kick in the bum needed to get stuck back into finishing off my CB250.

Would what he's done with the longer intake have the same effect as the "sleeves" even though he's still used the pods?

Cheers

NOZ

Probably work much better than restricting airflow with sleeves.
Total length is more important

That actually gives food for thought. Longer inlets tend to smooth the air flow as well as slowing it down. That makes me think that when a coke can is inserted to improve things, it may be the reduction in turbulence rather than just pressure differential that makes the difference.

Choking the inlet more than stock is unlikely to improve power, but it may change flow patterns. If it restricts flow then it probably lops 20% or so off the top end, but if you don't go there and don't measure it, did it ever happen?

I guess the way to test that would be to try cheap pods on a 3 jet Honda with a 4 way splitter to smooth flow and with the cheap filter set further back on a long tube to see the effects of both on rideability . I'd like to see some of these on a dyno to see what's actually happening and on a flow bench, but I'm not paying for that...

On mine I use 2" copper pipe that is the same size as the inlet, that way there's no obstruction for the air inlets . I dyno'd the bike without the extensions n it made 36hp to the wheel while being obstructed. Of course it was running super rich on the big end ( cause the pods block the top end air bleed)but the low n mid range was spot on. Haven't had a chance to redyno but should do it soon.

I might give it a shot as this really caught my eye when walking past. I hung around like a fly on a turd waiting to see if I could speak to the owner but no one showed up.

Also aesthetically it looks the goods.

Cheers

This thread is a very interesting read... I've been doing a lot of research on the Pod - CV carb issue. I keen to try out the alloy tube system as shown above & re jet to suit. I've found this very informative video on Youtube...

https://www.youtube.com/watch?v=y836ZPjvoMI&index=2&list=WLts4tFFtEAHYSdxJNvb90iQ

Couldn't watch entire video , BUT, giving numbers like 2.5, 5.0, etc is worthless.
You need a percentage increase.
Basic, for pods is 10% then adjust up or down in 2.5 steps
I'll use CB360 as an example because I do a lot of 360 carbs
CB360 starts with 100, goes to 110 but many need 112.5
Add another 5% for free flowing exhaust (CB360 - 115)
Another 5% if pipe diameter is more than about 20% larger than stock (most pipes are double wall, outer diameter is much smaller than the actual pipe inner diameter) (CB360 - 120)
A further 5% is needed if carbs are oversize to compensate for lower airflow over discharge nozzle
.....and, another 5% if you have short oversize exhaust system (CB360 - 125~130)
There are numerous other modifications needed to cure the excessive rich condition mid range when jet sizes are increased, 3 jet Kei-Hin carbs are a lot more critical on exhaust length, Mikuni not so bad and Hitachi a complete nightmare.
TK are similar to Mikuni

Holy S*** after weeks of beating my head against the wall trying to figure out why my bike was bogging hard, this thread just answered it all. I checked/tried literally everything trying to get this thing running properly, and turbulent air was the problem all along with the k&n pod filters. I tried putting the factory air box boots on, and voila. Bike runs perfect. So, that being said...... Here are the mods I made to my k&n pods. First off, I wanted to shorten them up for two reasons. 1- Clearance issues to my "fake oil tank" made them really hard to get on and off without scratching the paint, and 2- wanted to cut back some air flow to mimic factory air box. After cutting the pods open, I ground out the rest of the cloth/mesh filter from the chrome filter caps. I had some velocity stacks kicking around I shortened, and just happen to fit like a glove into the rubber boot of the pod filter. I RTV'ed them in, then ran a thick bead of RTV on the chrome end caps and glued them back on the ends of the filters. I already had tried the equalizer line between the two filters because supposedly, these bikes like a common air source, so I left that alone. So basically, I have pods with velocity stacks inside, and an equalizer line. Took the bike for a ride today, and its running perfect. Thoughts?

wtf is that on your exhaust pipe ?

did you ever even ride the bike in well tuned stock trim ?

Have you like, ever even heard of header wrap?
And yes, I did. Point being?

jap_scrap said:

Have you like, ever even heard of header wrap?
And yes, I did. Point being?

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no i was refering to the tubes with holes
as far as your filters you have created something with a great deal more restriction than any stock airbox
you are certainly losing a lot of horsepower on topend,because it takes air to make horsepower
did you ever even ride the bike in stock tune ?
that is, stock airbox and pipes ?

Machine gun exhaust tips, google it. Just simply drilled pipe. Without knowing the specs on the filters, or the velocity stacks as far as diameter, length etc., how do you know its a "great deal more restriction"? There's a lot more that goes into making horsepower than just air. Save your fingertips, I'm not going to start an e-pissing match with you.

jap_scrap said:

Machine gun exhaust tips, google it. Just simply drilled pipe. Without knowing the specs on the filters, or the velocity stacks as far as diameter, length etc., how do you know its a "great deal more restriction"? There's a lot more that goes into making horsepower than just air. Save your fingertips, I'm not going to start an e-pissing match with you.

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airflow volume is the single most important thing to making horsepower
you have fucked up the airflow at both ends but if it runs smooth and you are happy so be it
but you indeed greatly reduced the top end horsepower, i can tell that from here

So without asking me about jetting, any baffling in the exhaust, the air filters, velocity stacks, you've just up and determined that I'm losing power? Alright, I'm happy to know that dtt has a decent office chair mechanic.

jap_scrap said:

There's a lot more that goes into making horsepower than just air.

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I give up.

Was going to say something profound but can't be bothered :

xb33bsa said:

no i was refering to the tubes with holes
as far as your filters you have created something with a great deal more restriction than any stock airbox
you are certainly losing a lot of horsepower on topend,because it takes air to make horsepower
did you ever even ride the bike in stock tune ?
that is, stock airbox and pipes ?

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You'll probably find the total surface area of both K&N filters is similar to the single stock foam filter - BUT - both carbs breath through the single foam filter so the airflow is more than likely restricted with single K&N on each carb.
Using a fake oil tank ? May as well use the stock airbox and make some covers so it looks like a fake tank :

crazypj said:

You'll probably find the total surface area of both K&N filters is similar to the single stock foam filter - BUT - both carbs breath through the single foam filter so the airflow is more than likely restricted with single K&N on each carb.
Using a fake oil tank ? May as well use the stock airbox and make some covers so it looks like a fake tank :

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the stack stuffed up inside the cut down filter is the major restrictor that i see
the air is working too hard to find its way