Kawasaki VN750 Forum banner

1 - 20 of 34 Posts

·
Premium Member
Joined
·
3,027 Posts
Discussion Starter #1
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"
 

·
Premium Member
Joined
·
5,236 Posts
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.
 

·
Super Moderator
Joined
·
11,934 Posts
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
 

·
gun slinger
Joined
·
1,110 Posts
i like the bigger rear tire and






my uncle built a gazaboo
 

·
2FAS4U
Joined
·
469 Posts
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 :smiley_th
 

·
Premium Member
Joined
·
3,027 Posts
Discussion Starter #6
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.
 
  • Like
Reactions: roadpouring

·
Premium Member
Joined
·
3,027 Posts
Discussion Starter #7
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?
 

·
Super Moderator
Joined
·
11,934 Posts
You crack me up :smiley_th
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.
 

·
Captive New Yorker....
Joined
·
264 Posts
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?
 

·
Premium Member
Joined
·
3,027 Posts
Discussion Starter #10
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.
 

·
knees in the breeze!!!
Joined
·
498 Posts
if it was designed to perfection then they were 4ft 9 and had passengers that were a size 0 and 75 pounds
 

·
Premium Member
Joined
·
3,027 Posts
Discussion Starter #12
if it was designed to perfection then they were 4ft 9 and had passengers that were a size 0 and 75 pounds
Have you ever tried to ride a Honda Rebel? I had to sit on the "passenger seat" until I moved the pegs 4" forward.

Everything sold to the general public is a compromise, but it is the best compromise they could come up with. I can double the power of a sbc, if you don't mind leaving every stoplight at 6000 rpm. The Vulcan 750 has a good amount of power for it's size, and still idles like a kitten purring, yet will top 120 mph. When shifted at 6000-7000 full throttle, it will outrun pretty much any car. Not bad for a v-twin 750 cruiser.

It seems most everybody is doing the ear thing for purely cosmetic reasons. Which is good, because there is precious little extra power to be found in the VN750 engine without destroying it. It is already "tuned" as well as possible without becoming temperamental, finicky, and short lived.

Pod filters alter the delicate balance that was engineered into the intake, engine, and exhaust as a complete system. They actually lower power, as does an aftermarket exhaust. But my biggest problem with them is the amount of dirt the suck in. My bike has plenty of dirt on the outside (again this is AZ) but I sure don't want any of it on the inside.
 

·
Registered
Joined
·
856 Posts
This might be an interesting read for some...
http://www.knfilters.com/efficiency_testing.htm

Gives a rundown of K&Ns testing procedure and some numbers on their filters efficiency.
Now I'd love to see some data on the OEM foam filters as a comparison.
 

·
Dual Sport idiot
Joined
·
24 Posts
I might as well throw my two cents in here.

As far as CV carbs go, changing the intake path will not change the carbs performance. Simply put the carb works based on a combination of airflow (just like a standard carb), and uses the pressure differential across the throttle plate to adjust fuelling based on engine load. It's really a neat design. Removing the airbox can affect the pressure differential since the airbox is designed to help reduce the pulsing effect of the intake air. The only time you are likely to see a difference in performance is when the engine load is high but the rpms are low. The large volume of fuel with the uneven airflow can cause surging, however this should never be a problem since you would be bogging down your engine anyway.

As far as the performance of the Vulcan being anywhere near it's peak I can tell you with out a doubt that it isn't. The CV carb is the easiest way to tell. The main purpose of a CV carb is to maintain the air velocity into the engine, this provides smoother operation and allows the manufacturer to tune for emissions. With a manual slide carb the engine gets as much air and fuel as you want to give it when you want it there. The smooth running, high-performance engine only exists in the fuel injection world. I had a GTO that used to idle like crap and stunk like a gas station when you stomped on the go pedal. It was a lot smoother when I got it, but it was a lot slower too.

Now as far as the K&N debate goes; K&N filters suck. Period. No question. Oiled foam filters also suck. Paper filters are great but need to be huge to flow enough air. I'd never put a K&N filter on a car, but at the same time I've got a lot more room to work with. I can't stand cleaning foam filters, or oiling chains and cables either. I'm far more likely to clean and relube a K&N simply because they're easier to do. And as far as I'm concerned a properly looked after K&N is better for the bike than an under-maintained foam filter.

Hmm, I think I just talked myself into doing an earshave.

Oh, and in case you're wondering, I am a Mechanical Engineer and an Aircraft Maintenance Engineer and I might know a thing or two about engines.
 

·
Super Moderator
Joined
·
11,934 Posts
Jerry wrote:
"Pod filters alter the delicate balance that was engineered into the intake, engine, and exhaust as a complete system. They actually lower power, as does an aftermarket exhaust."

OK ...Now your just making crap up. It's been shown time and again, on dyno runs and lap times that increasing the air intake and altering the jetting to match increases engine power. I know for a fact that many aftermarket pipes do increase power on many bikes. Granted I have no figures on pipes made for the Vulcan 750...and would be willing to believe no one has built an exhaust for the Vulcan with performance in mind.

I too raced and tuned race bikes. I may have sucked as a racer, but a few of the bikes I worked on actually won races. You say you don't really know that much about motorcycle engines..... It's starting to show. ;)

It's just simple physics. A pod filter allows in more air. If you re- jet properly for this, you end up with a bigger charge of air/fuel per cycle... which creates a "bigger bang" and thus the motor will make more power.

Once you reach a certain saturation volume, the only way to get more power is to increase the size of the chamber, or physically stuff more mixture in with a turbo or super charger. You yourself said this.

As for are K+N filters bad? Compared to what? Have you tested their motorcycle filters? All I have seen is tests on car filters....and I have seen no test of the stock VN filter either.... So how can you make comparisons?
 

·
Premium Member
Joined
·
5,236 Posts
"To argue with a person who has renounced reason is like administering medicine to the dead" Thomas Paine, FWIW
 

·
Premium Member
Joined
·
4,778 Posts
Here is yet another reason not to use pod filters.
Jerry, I can't begin to count how many times I've seen you voice this opinion, along with your views on "dangerous electronics", how the VN7XX engine is too complex to rebuild (in spite of several threads here disproving that position), etc., etc., ad nauseam. We know your opinions, have no problem with you keeping them, but the sheer number of repetitions is mind numbing!

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.
What denny said! The reference to Don Quixote is very appropriate! Please, please give it a rest; for your sake and ours. I realize you don't mean it to be irritating, but that's how it comes across after the twentieth plus time you post it. It's like Chinese water torture. Here comes Jerry with the same old, same old - again! ARRRRRGGGGGH! :dead_hors:dead_hors:dead_hors

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.
The reason folks are upset by some of your posts is becasue 1. they hear the same things so often, and 2. in a number of instances your opinion has been proven not to be accurate/factual! When you continue to espouse those disproven opinons as fact, folks cease to take you seriously.
 

·
Premium Member
Joined
·
1,803 Posts
"To argue with a person who has renounced reason is like administering medicine to the dead" Thomas Paine, FWIW
Good quote. Here's another " Being a contrarian doesn't necessarily mean you're wrong and should be ignored " JM2001 :)
 

·
Premium Member
Joined
·
117 Posts
My 2 cents!
Not everyone is "upset" with Jerry's opinions. Although I often do not agree with his opinions, I find his posts interesting and thought provoking. Unlike posts by some on other forums, his posts are not abrasive. If you don't like his posts, don't read them. If you disagree, politely respond with an alternative opinion.

With regard to repeating a topic - it is often worthwhile for newcomers or infrequent visitors to the forum. Many users do not have a specific problem to address (search), but just review the most recent posts. I have gleaned much useful information this way on this and other forums.

I understand that long time members become jaded with repeatedly responding to the same question from newbies or repeated opinions from other members, but I think that is part of the vitality of this forum.

I value the opinions and advice of Jerry, KM, Gordon, Denny and many others and hope no one is deterred from posting or leaving this forum.
 

·
Premium Member
Joined
·
5,236 Posts
My 2 cents!
Not everyone is "upset" with Jerry's opinions. Although I often do not agree with his opinions, I find his posts interesting and thought provoking. Unlike posts by some on other forums, his posts are not abrasive. If you don't like his posts, don't read them. If you disagree, politely respond with an alternative opinion.

With regard to repeating a topic - it is often worthwhile for newcomers or infrequent visitors to the forum. Many users do not have a specific problem to address (search), but just review the most recent posts. I have gleaned much useful information this way on this and other forums.

I understand that long time members become jaded with repeatedly responding to the same question from newbies or repeated opinions from other members, but I think that is part of the vitality of this forum.

I value the opinions and advice of Jerry, KM, Gordon, Denny and many others and hope no one is deterred from posting or leaving this forum.
I don't want to deter any one ,that's for sure,I admit I enjoy hounding Jerry and KM and occasionally Ol Hoss from time to time but I like almost everyone on here and I do it for fun.I live alone and the dog doesn't care what I say to him. It doesn't bother me at all to answer questions that have been asked before.Shoot,they are the easiest to answer!
 
1 - 20 of 34 Posts
Top