REAL guru question

[xschop]

When you guys put pod filters on, you say you need to rejet. More than likely because of the increased filter area, or due to removal of the velocity stacks from carbs to air box? Reason why I'm asking is I am designing a 1-piece filter that disassembles with one or two screws and gets rid of the air box. The filter that is the best fit is only 1.75" tall and I would need to trim down the part of the velocity stacks( ends inside stock airbox).....INPUT?

[egsols]

Correct me if I'm wrong but isn't the reason behind rejetting after installing pods to ensure that you don't run the bike too lean with the increased air allowed by the pods?

[prometheus578]

"The Pod People."

Carbs function on a delicate balance.
The piston moving downward creates a low pressure area, commonly called a vacuum.
Now then... this vacuum sucks... and wants to be filled with air, which is supplied through the throat of the carburator.
If the vacuum in the cylinder has a value of "X", then the air flow through the carburator should have a value of "X".
Now then... suppose the carb throat has a little straw sticking up in it, and this straw is dipped in a bowl of gasoline.
Also suppose, that at the far end of the carb throat, there is a restrictive element, let's call it an air fiter.
So... the piston moves downward creating that vacuum thing of volume "X".
Air wants to be sucked into the cylinder through the carb's largest opening to fill that "X" volume, but due to the restrictive filter, there's a problem. The air doesn't move quick enough to fill volume "X". What happens then, is some of the vacuum from the downward piston movement acts upon the straw and actually sucks up some of that gasoline from the bowl.
Can you imagine that?
So, in a perfect world, (like the one Pat Kelly lives in)... as the piston moves downward, it sucks in a predetermined fuel mixture. (Part air, part gas, as determined by the restrictiveness of the air filter and the size of the fuel jets.
(I failed H.S. algebra, so I can't do the fancy schmancy equations, but that "X" volume is made up of something like 15 parts air and 1 part fuel.)
Now, some people think they are smarter than those Japanese engineers. They want to put on free-er flowing air filters.
This is all fine and dandy and is their right.
But what happens is... the free-er filters are less restrictive. They allow the air to move through easily, and thus the vacuum in the throat area is reduced.
This reduced vacuum then is insufficient to raise the proper amount of fuel through that little straw.
Now, we have a LEAN fuel mixture, and the bike runs like doodoo.
What to do... what to do...?
What one does then, is to rejet.
One rejets... going up to larger sizes of main jets, sometimes pilot jets, or sometimes just turning the pilot screw open a little more.
This increases the amount of fuel available...making it easier for the "new air filter" reduced vacuum "to suck it up".

Velocity stacks provide a nice even air flow... Wikipedia knows all about it, and if you read the article, then so will you.

THE END

[xschop]

what if

what if one (being me) is putting in an 80 head and 79 cams with this filter? school me prom

[prometheus578]

"I only teach "gifted" students...

... "Special Ed." is down the hall.

[prometheus578]

Sadly, everything is trial and error... mostly error.
Any deviation from the original requires a modification somewhere, to some degree.
Could be a large degree or a small one.
Anyone who makes changes needs to realize that they will be tinkering for a bit afterwards.
Why does the XS1100 G take #115/#120 main jets and the XS1100 SG takes #110/#120 jets? Who knows?
There are differences between the 79/80 configurations: valves, combustion chambers, etc.
Too many variables for this non-engineer to figger out.
All one can do is rely on the advice of those who've travelled that route before and what has worked for them.
(I haven't travelled far, and in fact, barely leave the house.)
Make your mod, XSChop..., then read the plugs and see what the engine's telling you.

[xschop]

air filter

this first two filters shouldn' be that much of an increase in filter area as compared to stock, definitely not as much as Pod filters
http://www.knfilters.com/search/prod...px?Prod=E-2880

http://www.knfilters.com/search/prod...px?Prod=E-2970

[SanDiegoMike]

As usual Prom, your input is riddled with dry humor and very informative to us minions hoping to achieve a deeper understanding of the operation of these awesome machines. Thanks for the schoolin'!

[prometheus578]

"This is a restricted area!"

XSChop...
While it does matter a bit... the size of the filter area isn't the issue.
How free flowing the filters are is what matters here.
There are some bikes, mostly two-strokes... that if you take the filters off, the bike won't run at all!
A larger surface area of a filter just means it can trap more dirt before it gets too plugged up to function properly.
K&N pod filters, for instance, have an oil impregnated cotton filter element. Very free flowing.
Cone shape is eye appealling and provides a large surface area to trap dirt.
I can get the same effect by using a hose clamp and strapping a torn piece of my black t-shirt(oil inpregnated, of course) across the throat of the carb.
The smaller surface area will get dirty quicker... and then I'll have more laundry to do.



Hey XSChop...
It's 11:00...
I mean... I've been sitting here all morning...
Would it be OK if I turned off the computer, jumped through the shower, put on a T-shirt that didn't have little squares torn from it and start my day?
I sort of had things I wanted to do, ya know?

[xschop]

I suppose

You must live in La La Land (Cali). It's 1:30 here in Okie ville....I will do just that and start this mod. I am sick of removing the XS11 airbox to get the carbs out easy, Should only take two screws and yer done. I have the KN filter (STOCK XS11 SHAPE) in the airbox (I didn't have to rejet when I put that one in). I figure this filter is not much of an increase in area (ALSO K&N BRAND). I see the limiting factor of the stock system is the XS11 snorkel tunnel... Will look like this and be EASY to take off....

[egsols]

Okay, its a given that the air flow through a filter is dependant on the porosity of the filter medium. One question though, as the stock box has the small snorkel under the seat as its intake, wouldn't a stock filter, uncovered, allow for a sustantial increase in air due to the larger intake area?

[xschop]

irish spring

Give the man time to wash his #&%#@*! A True Guru takes his time in the john to ponder such knowledge. Seriously I was thinking the same thing Egsols. But unless "one" had a flow bench and put the snorkle up against the stock filter "one" wouldn't know the difference. I remember installing the K&N and getting better throttle response and low end pull, so the stock filter was the limiting factor. I will be doing this for ease of maintenance, however I will install it before I do the 80head/79 cam install to see what's the deal...chop

[prometheus578]

"Sorry, I was in the bathtub, playing with my snorkle."

If you look at the size of the opening of the snorkle... yes, it is part of the airbox flow restriction set up.
You will find mention on this site of "drilling holes in the airbox".
This helps provide more airflow... more than what would be able to conveniently pass through the snorkle, Hence a free-er flowing system.
The air box, with it's snorkle and velocity stack carb inlets was designed to do more than just hold all the parts together and keep out dirt and dead bugs.

[customaxe]

Prom.. there's something very disturbing about you " impregnating " you're oiled up t-shirt .. I can't quite put my finger on it .. but it's there... anyway ROCK on Prom.. I'm going to go to my basement and get a date for tonite ..

[skids]

Re: "Sorry, I was in the bathtub, playing with my snorkle."

What about...drilling holes in the SNORKLE! (just kidding)

Originally posted by prometheus578
If you look at the size of the opening of the snorkle... yes, it is part of the airbox flow restriction set up.
You will find mention on this site of "drilling holes in the airbox".
This helps provide more airflow