pod filters - Kawasaki Vulcan 750 Forum : Kawasaki VN750 Forums
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post #1 of 34 (permalink) Old 03-28-2012, 06:08 AM Thread Starter
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pod filters

Here is yet another reason not to use pod filters. Most of my tuning experience has been with carbureted American car engines, I have very little experience with bikes, especially street bikes. I've always known that pod filters let a lot more dirt through, but here is something else I never even thought of, regarding their use on newer motorcycles. This is a post from another forum, form someone who does know something about motorcycle tuning.

"The big issue is that most carbureted bikes from the '80s on up, uses Constant Velocity carbs. The throttle controls only a butterfly valve. The slide and jet needle, which affect air flow and fuel metering, operate by a vacuum diaphragm that is controlled by negative pressure within the carburetor throat (venturi). It's a clever design, intended to keep the engine from bogging when the throttle is whacked open, but it's designed to work as a system with the airbox. So, switching to pod filters not only affects the fuel flow through the pilot and main jets, but also throws the slide calibration out of whack. Good luck trying to retune to compensate for all of that"

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
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post #2 of 34 (permalink) Old 03-28-2012, 07:43 AM
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Quote:
Originally Posted by VN750Rider/Jerry View Post
Here is yet another reason not to use pod filters. Most of my tuning experience has been with carbureted American car engines, I have very little experience with bikes, especially street bikes. I've always known that pod filters let a lot more dirt through, but here is something else I never even thought of, regarding their use on newer motorcycles. This is a post from another forum, form someone who does know something about motorcycle tuning.

"The big issue is that most carbureted bikes from the '80s on up, uses Constant Velocity carbs. The throttle controls only a butterfly valve. The slide and jet needle, which affect air flow and fuel metering, operate by a vacuum diaphragm that is controlled by negative pressure within the carburetor throat (venturi). It's a clever design, intended to keep the engine from bogging when the throttle is whacked open, but it's designed to work as a system with the airbox. So, switching to pod filters not only affects the fuel flow through the pilot and main jets, but also throws the slide calibration out of whack. Good luck trying to retune to compensate for all of that"
so ,since you nor this guy have figured it out,no none else has?Sorry Jerry,Tell him if he needs help .We're Here for him,we have.We all understand you don't like K&N filters,But I am just curious why you want to keep Jousting with this particular windmill.

If you want to pick a cause to crusade for, make it something worthwhile like Feed the Children or something ,The one or maybe now ,2 man, war on K&N filters is bordering on an obsession.You don't like K&N .We get it already.Others do and you are wasting your time worrying about what someone does to their bike.It is not my concern,example:I don't like Ape Hangers on a bike,but if anyone else does ,I could care less .Live and let live.




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Last edited by denny6006; 03-28-2012 at 08:43 AM.
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post #3 of 34 (permalink) Old 03-28-2012, 08:39 AM
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All stock carbs are designed to work with the stock airbox. Fuking Duh.

You change the air intake, you need to change the fuel metering. This is why there's a list of reccomended jetting changes you have to use when you switch to pod type filters. Another DUH there.

CV carbs adapt to ENGINE vacuum...and try to suck in the needed air through whatever air intake you use. It's not the other way around. Add more air and you need to add more fuel.... Believe it or not it is as simple ad that....


And another DILLIGAF . And DILLIGAF what some clown in another forum thinks either?

Although about scooters, a good explanation on how CV carbs work:
http://battlescooter.com/1.html


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Last edited by Knifemaker; 03-28-2012 at 10:42 AM.
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post #4 of 34 (permalink) Old 03-28-2012, 10:58 AM
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i like the bigger rear tire and






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post #5 of 34 (permalink) Old 03-28-2012, 11:30 AM
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Quote:
Originally Posted by Knifemaker View Post
All stock carbs are designed to work with the stock airbox. Fuking Duh.

You change the air intake, you need to change the fuel metering. This is why there's a list of reccomended jetting changes you have to use when you switch to pod type filters. Another DUH there.

CV carbs adapt to ENGINE vacuum...and try to suck in the needed air through whatever air intake you use. It's not the other way around. Add more air and you need to add more fuel.... Believe it or not it is as simple ad that....


And another DILLIGAF . And DILLIGAF what some clown in another forum thinks either?

Although about scooters, a good explanation on how CV carbs work:
http://battlescooter.com/1.html


KM
You crack me up
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post #6 of 34 (permalink) Old 03-28-2012, 11:52 AM Thread Starter
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Why is it everybody gets upset about my opinion when there are several people on here who openly advocate doing the "earshave" thing, and recommend it to beginners, without explaining the consequences? I have done a couple of mods to my bike that work perfectly for me, but I am NOT recommending them to anyone else, because there COULD be possible consequences, especially for a beginner.


While I am NOT a motorcycle tuner, I do know that stock motorcycles, especially high performance motorcycles like the Vulcan 750, are highly tuned by design. And they were designed by an engineer (actually likely more than one). They have been tested and retested. Their tuning has been refined to be as close to perfection as the engineers could get it. I am NOT an engineer, but I do rely on information from them when I work on such things.

By the way, the guy that posted that is both a roadracer and race engine builder with lots of experience.
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I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #7 of 34 (permalink) Old 03-28-2012, 12:24 PM Thread Starter
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Quote:
Originally Posted by Knifemaker View Post
All stock carbs are designed to work with the stock airbox. Fuking Duh.

You change the air intake, you need to change the fuel metering. This is why there's a list of reccomended jetting changes you have to use when you switch to pod type filters. Another DUH there.

CV carbs adapt to ENGINE vacuum...and try to suck in the needed air through whatever air intake you use. It's not the other way around. Add more air and you need to add more fuel.... Believe it or not it is as simple ad that....


And another DILLIGAF . And DILLIGAF what some clown in another forum thinks either?

Although about scooters, a good explanation on how CV carbs work:
http://battlescooter.com/1.html


KM
Just curious. Do you have pod filters on your FJR? Have you made any intake or exhaust mods to it at all?

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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post #8 of 34 (permalink) Old 03-28-2012, 01:19 PM
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Quote:
Originally Posted by 2fas4u View Post
You crack me up
Quote:
Originally Posted by VN750Rider/Jerry View Post
Just curious. Do you have pod filters on your FJR? Have you made any intake or exhaust mods to it at all?
No. But i have oiled foam "pod" filters on my project Vulcan. They were there when I bought the bike. The bike ran great. LOUD..... But noticeably faster than my stock 750.

Have have no issue with the post by the "racer" other than him saying pod filters throw the "slide out of whack". CV carbs work their best when the intake air is at atmospheric pressure. They actually rely on this to work. Unrestricting the air intake will in fact make the carb work more efficiently.

2nd...bike is not designed to run perfectly by engineers from the start. They unfortunately have to make concessions with EPA, other government regs, and marketing concerns.... Which ends up making the bike a compromise. I once asked a Yamaha rep why they just didn't tune their bike with simple bolt on airfilters and he listed everything from noise to liability do to higher chances of engine fire. So sorry, no stock motor is designed with complete performance perfection as the main goal.

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post #9 of 34 (permalink) Old 03-28-2012, 03:05 PM
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I bought K&N filters to replace the stock filters in the ears. I'm leaving the ears in place. Am I going to have to adjust the carbs to use these new filters?



Pete Herrmann
1994 Vulcan 750 40K on the clock and counting....

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post #10 of 34 (permalink) Old 03-28-2012, 03:24 PM Thread Starter
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I bought K&N filters to replace the stock filters in the ears. I'm leaving the ears in place. Am I going to have to adjust the carbs to use these new filters?
Probably not, the little square hole in the air filter is the most restrictive thing in the intake system. Just be aware the K&N filters are more porous, and will allow more dirt to pass through them. Of course, unlike pod filters which are completely open, the filters inside the ears are protected from a lot of dirt.

I would never use K&N filters here, the air is always full of dust. You can wash your bike one day, let it sit outside for 24 hours, and write your name in the dust on the tank.

While the little square holes are pretty restrictive, there is suction there, from engine vacuum, so it will suck in any dust that gets close to the holes. Best to keep those filters soaked with as much oil as they will hold without dripping.

I am a motorcyclist, NOT a biker.


1997 Vulcan 750, purchased about a week ago
2006 Sportster 1200 Low
2013 Royal Enfield Bullet 500, converted to carb
2001 Yamaha XT225, heavily modified
2004 Honda Rebel 250
1979 Vespa P200E
2002 Vulcan 750 parts bike
1994 Yamaha XT225 parts bike
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