Does Changing an Air Filter in Bike Require Rejetting?

Only if the pressure drop through the new filter is substantially different from before.

Very unlikely. Anyway. Why not just swap it with a clean, like-for-like replacement and save any hassle (rhetorical question - NNTR)?

The re-jetting of a fuel system is only needed if you change the cam, cylinder size, or increase the altitude that you operate in. Changing the filter will not make the engine take anymore volume then it is designed to take in. 100 CC's is 100 CC's.

Altitude? I bought my bike in Norfolk UK, and am now living at just under 4000ft. Should I consider jetting my 2000 cbr 600? (I have a k&n also).

Drew K

Generally speaking motorcycles are tuned to run at sea level, for increase in altitude of every 2000ft, size of jets should be reduced 1 or 2 increments....less oxygen , less gas, less power.....You might be able to keep the same jets by installing a less restrictive air filter, as mentioned, and reduced exhaust pressure, by installing different pipes...or pulling baffles....this is just ballpark, and a mechanic should be consulted for final settings.....

http://www.ehow.com/how_7668889_tune-carburetors-altitude.html

Well, then I am good! I have a K&N filter and an Art race can on (she is a bit loud when I get on it).

Drew K

A lot of carbureted bikes, especially 80's vintage were notoriously lean from the factory (thanks EPA), and will have much better running (but lower power) at higher altitudes because they get enrichened so that off-idle stumble disappears, warms up better when cold, etc.

If you are simply swapping the stock air filter element for a K&N replacement, then no jetting changes should be necessary. If you are removing the stock air-box and installing some type of high-flow/racing-style filter then rejetting will almost certainly be required.

I'm sorry,

On this one from my own personal experience, all the answers you have gotten has been wrong.

I also have put K&N's on all the bikes I ride and on every one of them I HAD TO RE JET them. or they ran too lean. The vacuum pressure at the jet is much lower with the K&N's that the stock systems.

So much so, that until the new jets arrived i had to run the bikes with some choke applied get the bikes to run right again, the vacuum at the jets were that much lower with the K&N's

See Pantaz right above. I'm with him, if you keep the stock airbox and intake plumbing, it's very unlikely you will have to re-jet unless the bike was already leaned out the kazzoo to begin with. Ditch the box and put on individual filters, yes absolutely. I did it with my 1970 CB750 twenty-five years ago. Along with the Kerker 4-1 and a few other tuning goodies. My older brother still has the bike with about 80k on the clock.

I've put K&N in a stock box and have had no problem with the jetting. Even did the WOT-kill switch-clutch plug checks.

It depends on which carb type you have. If it is a basic slide type, then you may need to raise the needle in the slider up one notch. If it is a CV type with a diaphragm and spring that raises the throttle piston then you should not need to make any adjustments.

You can tell one from the other type by the larger cylinder and cap at the top of the carb for CV type carbs, and a throttle cable coming into the top for a basic slider type.

I'm always amazed at the casual "expertise" evidenced by owners who presume the designers of the carburettors were bumbling fools. Intake restriction is part of carb design, as is exhaust restriction. But carry on. It's not like bikes are necessary objects. All you can do is cost money pursuing ephemera.

It has nothing to do with the designers'/engineers' expertise. They are tasked with facilitating the best compromise of performance, economy, manufacturing cost, emissions compliance, and even noise limits. (Intake sound levels can have a significant impact on motorcycle noise measurements.)

Changing intake and exhaust components can be a quick and inexpensive way to "tune" an engine. Done wrong, it can also "de-tune" an engine. My first attempt, when I was young and didn't know what I was doing, was a disaster. With help from a good local shop, I learned how to correct it and ended up with a bike I loved.

This is exactly, what it is all about. The whole system. Changing anything in the flow of the engine changes something else. Now even like someone else stated, exhaust matters just as much too.

Like while many think it is cool sounding the open drag pipes on a V twin engine. what many do not realize is most times they are loosing power!

How can pipes with absolutely no restrictions cause you to loose power/

This video explains it very well

http://www.youtube.com/watch?v=KjKUKhHQLHg&feature=share&list=PL172D8BF755A526E7

It still comes down to volume in volume out. You can only get so many cc's through a given size. Do the math! To change the flow as I stated before something has to change. That's why racing folks port polish and enlarge ins and outs.

Jeez guys. What a bunch of engineers. The guy has a simple question for a simple mod on a simple engine using an off the shelf part engineered to be off the shelf.

I used to be a motorcycle mechanic and putting a K&N on a single to replace a paper filter is not rocket science. The air flow will increase, but that increase will only affect the carb if it is a basic slider type carb. A CV carb balances it's own air flow and so rarely will it require rejetting for such a minor change. The new filter will increase top-end performance with better flow and low end performace with easier flow.

I'll say it again, he might have to raise the needle a notch if it is a basic slider. That's it.

I don't think changing the air filter will require re-jetting the carb. A K&N filter or any filter will gradually reduce the air flow through the element because a filter works by blocking particulate matter in the air and that will change the air/fuel mixture as more of the pores in the filter are blocked.

Hi Folks,most modern Bike Carbs do Run very Lean,the key would be the amount of Air that can de drawn when using a stock Airbox.If a K&N is fitted to a 1200 Bandit for example the Box can't draw enough to supply too much unless a mod is made to take advantage of the higher flow. Airbox volume has increased dramatically since the 80's as Bikes are now designed more with induction in mind.My 80's 1100 has the same size Airbox as a later 250 ! Cv's are very good but are set Ball park for countries and emission control (Asthmatic Harleys in the UK because of US controls Ect)Generally Fitting a higher flow filter may benefit from raising the Needle a notch or two and a tweek on the Air Screw (capped for US)Specially with a High flow Can. When fitting individual Filters to each Carb a Jet change is usually inevitable.If you don't have a Dyno to hand best to start Rich and work down to avoid Engine Damage.I have found a clash of terminology in the past whilst discussing Rich/Lean,some (less nowdays) People relate to rich/lean as Air Fuel (cars) and others relate to Fuel Air (Bikes) this could cause confusion and expense to an enthusiastic bystander/Novice.Most bike Tick over's now are 1000 to 1200 Rpm as a rough guide for Jap stuff.Best thing is to Google a Forum or the Supplier if in any doubt and it would be quicker for set up and cheaper than a wrecked motor.

Thank you guys for your replies....

some of them helped me :))) i changed the filter....and i had a test ride....before changing the filter i was able to go upto 120kmph and after changing its going 110kmph....nd no tuning is done in carb :))) nd now my bike has increased pick up with awesum roaring sound :D

So you are going slower now with the new filter?

Drew K