How to: Fit a K&N Filter and Rejet a Carburetor

by Deepak on February 4, 2010

This post is for all my fellow bike riders who wish to extract the last possible juice out of your ride. This post is regarding to the fitting of free flow air filters, its effects and how to rectify it using the method of re-jetting.

You need to consider re-jetting your bike whenever there’s been a major change to the air intakes (like installing K&N filters which allow more air to pass to the carburetor), or adding drag pipes. Both modifications will lean out the air-fuel mix. The stock jet can only allow a certain amount of fuel to pass through and is designed according to the specification of the vehicle. Installing larger jets increases fuel to the carburetor to restore the 14 parts air to 1 part fuel optimum mix. This mixture is called stoichiometric ratio. Whenever the amount of air intake is increased, the fuel part is also to be increased. In all other cases, the stock jets will take you through 95% of your riding requirements.

Since the main jet effects all speed ranges after idle, you need to get the main jets right first, and then tune the mid-range and low end. All tuning should be done on a fully warmed up engine because that’s the way you usually ride; the spark plugs should have been previously checked and cleaned; the gas tank should be at least half full; a new or recently installed fuel filter if present; the air intake filters checked for holes, and cleaned; and all air intake and manifold connections tight and secure; the battery fully charged; and the carburetors synchronized, if it’s a multiple cylinder engine (more than one cylinder, eg: kinetic comet ) for optimum results.

We are now going to tune the carburetor without the help of a tachometer (engine speed). High speed or top end main jet sizes are determined by full open throttle performance. Low and mid-range tuning is determined mainly by how the bike feels to you as you roll the throttle. Mikuni CV carburetor is different from the Keihin CV. So is the difference with other carburetors. So tuning will be different in different vehicles.

Note: If you do sense a loss of power, or rough running on a stock vehicle, it may due to some other reason. In this case re-jetting is not the solution to the current problem. Please take the bike to an authorized mechanic and rectify the problem.

HIGH SPEED JETTING

High speed performance (80 KPH and up) is controlled by the main jets. To make sure you have the right main jets, take your bike out to an open highway where you can safely (and legally) open the throttle all the way in top gear. Ride the bike full open and let the bike get to top speed. Again, do this only if you are experienced and comfortable running at top speed and you are not in danger of injuring yourself or someone else.

A. If at top speed or before, the bike runs rough, heavy throttle feel or begins to hesitant and buck, your main jet is TOO BIG. The mix is too rich (more fuel than the optimum 1 part fuel to 14 parts air) and you are getting an uneven burn and poor performance. Install smaller main jets and take the bike for another test run. Another way to determine rich mixture is, when u cold start the vehicle and if the bike starts in the very first crank the mixture is rich (no need to use the choke in this instance). Low fuel efficiency and more smoke in the exhaust than usual are some of the characteristics of a rich mixture.

B. If before top speed the engine is running smooth, but has no power, seems to be running hot or knocking from the engine and you can’t push the bike to top speed, then your main jets are too SMALL. You are running too LEAN a mix (less fuel than the optimum 1 part fuel to 14 parts air) for maximum engine performance. Put in LARGER main jets and take the bike out for another test run. Another way to determine lean mixture is the difficulty u feel when cold starting. Even after repeated cranking, if the engine does not start, the mixture is lean. When u closes the throttle in a downhill, if u hears popping or cracking sound from the exhaust, it is again due to the lean mixture.

MID-RANGE OR MID-SPEED TUNING

The carburetor needle controls mid-range performance. The needle tapers down to a point that fits into the main jet. The needle is lifted upward (along with the slide) by the carburetor diaphragm as the air flow increases through the carburetor. As the needle moves upward it is withdrawn from the main jet, allowing more fuel to mix with the increased air volume. All that is needed to modify mid-range performance is to place (or remove) one or more small, thin washers between the diaphragm and the head of the carburetor needle where it’s held in the diaphragm. Adding washers effectively raises the tapered needle further out of the main jet at all engine rpm’s and allows more fuel to mix with air to create a richer mix. Removing a washer effectively leans out the air-fuel mix.

There’s usually no need to replace the stock needles since they have proven over time to provide good performance and good gas mileage. If you do use a third party needle for increased performance, then anticipate lower fuel efficiency.

Mid-range tuning is accomplished mainly by how the bike performance feels to you. If there’s a smooth increase in power as you roll the throttle, then you’re there. If there’s a slow response or there’s no power, then the mix may be too LEAN and you may need to add one or more washers to richen the mix. If the bike accelerate with power, but feels rough, you may be too RICH and need to remove one or more washers to lean out the mix. Now take the bike out for a test spin.

LOW OR SLOW SPEED JETTING

Now you can tune for low end performance. If you are getting a poor pickup or hesitation off the line, or a lot of backfiring on deceleration, then you need more fuel through the pilot jet. You increase fuel flow through the pilot jet by turning the pilot jet screw OUT a half turn. It’s best to start at 2 1/2 turns OUT on the pilot screws and then increase the turns OUT 1/2 turn at a time, and go for a test run. Do these until you get the performance you want and/or there are no back fires on deceleration. If you go more than 5 or 6 FULL turns out, you will probably have to install a LARGER pilot jets. Larger pilot jets are usually needed if you have removed the stock air intakes, air box and installed K & N filters which dramatically INCREASE air intake volume.

I am not posting how to successfully repair the carburetor because of its complexity for a normal person. And friends, please make sure that a professional mechanic is always nearby if anything goes wrong.

GENERAL PROBLEM SOLVING TIPS:

If you get inconsistent running, fluctuations in power, you are probably running rich. Lean running is more likely to cut power completely. If you have poor power at small throttle openings and a surge at wider throttle then you may be running lean. Quick ways to see if you are running rich or lean.

* APPLY CHOKE AFTER WARM – UP TO ARTIFICIALLY RICHEN THE MIXTURE.

If you bike runs better with the choke on even after a few minutes of warm – up, your original mixture might be lean in the lower rev range. This test does strange things to the upper rev range, so don’t use it at highway speeds.

* REMOVE THE AIR FILTER COVER AND ARTIFICIALLY LEAN OUT THE MIXTURE

Temporarily remove the air liter cover (to INCREASE air to the mixture), and go for a test ride. A well tuned bike (where the air and fuel mix is right on) will run pretty badly (i.e. mixture too lean) when you do this. But if the mixture was originally too rich, the bike will run better. Then u can fix the air filter cover and lean the mixture.

If your bike’s performance has a hitch or hesitation at certain speeds or you can’t tell if it’s rich or lean, experiment by leaning out the mixture which is the easiest way to find out – if the mixture was originally too rich, the bike will run better immediately. If the mixture was originally too lean, your bike will run worse immediately

(Use the tuning techniques listed above to adjust the low, mid- and high speed ranges).

Now u might also understood why manufacturers stick to a particular setting and not going for extreme tuning. Extreme tuning will call the need for extreme keeping up of it. Friends, it’s all about experimenting with different settings. Also if found a good setting, don’t forget to check the fuel economy too. And always ride safe! :)

- Abiram Menon

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{ 54 comments… read them below or add one }

fas February 4, 2010 at 7:12 pm

That is a very informative article. Great stuff.

@Deepak this should be sticky :P

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sword February 4, 2010 at 10:11 pm

nice article really helpfull

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Deepak February 5, 2010 at 8:16 am

We expect more articles from you!

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Puneeth Keekan p February 5, 2010 at 11:38 am

This is a very good educative article for Indian Bikers.I checked out almost all the contents in this site.Its really much more than what i really expected..I appreciate your efforts..Thank You very much Team Bike Advice..You people are doing a great job..:-)

Regards
Puneeth Keekan P
Mangalore

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Deepak February 5, 2010 at 12:01 pm

Thanks Puneeth!

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Rathish February 5, 2010 at 7:19 pm

Thank you Abiram, thank you thank you very much. This is what i am looking for so many days so I do not have any one who can explain it to me in this manner. Just last week, last made a comment in this blog, hope you might have read it. Looking forward with lots of other technical stuff from you. Thank you for Deepak too, very much as being an inventor of this blog.

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Deepak February 5, 2010 at 8:37 pm

You are welcome Rathish! Your encouraging words gives us positive energy to make this blog better every day!

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Abiram Menon February 5, 2010 at 9:07 pm

As Deepak said, your encouraging words are the fuel for my ride…thank you for all the comments since it is my first post :)
And friends, pls if u found any doubts or u have any quires, pls post comments as this is one of the area in which people flounder the ride by fitting a K&N filter.

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suhas February 9, 2010 at 1:20 pm

wats the preferred jet size for yamaha fz16 after i ve fitted in the KN filter, kindly revert back as i m facing the starting problem as well as the coughing sound from exhaust and drag especially from 60-80 range

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Abiram Menon February 9, 2010 at 5:25 pm

Hi, Suhas..Where have u fitted the K&N filter? i mean is it fitted directly to the carburetor or in the air box? The problem seems to be a very lean mixture. Do a proper engine tuning by a good mechanic. Please try to find a reputed Yamaha mechanic.If u still face problems after the retuning, u have to change the jet to a bigger size. I am not sure abt the jet size, but a competent mechanic can do this work within half a day. Otherwise try to source a Iridium spark plug and splitsfire cables which will burn the lean mixture efficiently.What my mechanic asked me was to bring him a spare main jet.I think, he took it to lathe or something as bigger jets is not there for Karizma at that time.The after effect was awesome.Can beat a P220 simply.

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aditaya February 17, 2010 at 5:46 pm

plz tell me which jet i use to r15 after fitting k&n filter

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G.Nepal Reddy March 18, 2010 at 2:54 pm

1.What is the HP? 2.How to Deside HP in vehicle or bike? 3.What is the TOURQUE? & How to deside Tourque? Please explaine me.

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Abiram Menon March 18, 2010 at 5:05 pm

@Aditya: R 15 uses fuel injection, there is no jet in a fuel injection vehicles so at present u cannot change anything to modify the performance of the vehicle. there is performance modification like ECU upgrade and high lift cam and Free flow exhaust which is Yamaha providing in the Daytona performance kit. The kit is costly though.

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Abiram Menon March 18, 2010 at 5:10 pm

@ Reddy: Hp is the horse power produced by an engine. Brake horse power is the power produced minus all the losses like frictional. 1 horse power= 768 watt. torque is the twisting force produced by the engine. If simply said, Torque decide the pulling power of an engine and BHP decide how fast that pulling power is produced. So Torque is an important aspect alongside with BHP.

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h2k March 29, 2010 at 9:56 am

Hi Abiram,

Its very informative article. I’m planning to buy Suzuki GS150 R this week. Can I use K&N in my Suzuki GS150R. Will it affect my engine life. When can I put it, during run-in period or after that. Please advice me as I’m so impressed of the performance of the K&N Air filter. Once again I appreciate your great work :-)

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Abiram Menon March 30, 2010 at 12:55 pm

hi, h2k
u can fit k & n filter on ur bike. But ill recommend u to put it once ur run in period is over, or atleast some 3500 km. even though there is no problem fitting it on a new bike, lets keep it a new one as possible. So no Modifications before that.
have a safe drive.

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siddhu April 9, 2010 at 2:13 am

hey guys can anyone tell me abt a well experienced mechanic..coz i’ve installed k&n filter on my fz16 after usage of 8000 kms..now the pickup is good but. Its not lifting upto the high speeds as long back..previously my one can drag upto 115 but now its dying to get 110. Can anyone tell me any mechanic was der to figure out my problem..i need my bike to jet it..so please suggest me a good mechanic who can do this stuff without messing..
I’m living at vijayawada, andhra pradesh(state)
My mobile number is +919505698819
You can leave an offline msg at siddhu_thesolid@yahoo.co.in
Guys pls reply with a good suggestion..

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siddhu April 9, 2010 at 2:17 am

hello abiram..pls suggest me yar..i can’t drive my bike in that coughing position..

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Abiram Menon April 9, 2010 at 10:23 am

Hi Siddhu,
The problem is just because ur bike is getting a lean mixture. That is exactly the reason why more power and smoothness in low speeds and exactly the opposite in high speed runs. U can try tuning the carburettor from a good workshop. If tuning is at its maximum, u have to change the jet to a bigger size. I am sorry tat i dont know any mechanic in Andhra, but try Castrol bike point. It will be there in your town.

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siddhu April 13, 2010 at 12:01 pm

thanx abhiram for your concern

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appu348 January 23, 2011 at 10:02 pm

hai friends i am new hear i have a yamaha libero bike
i want to improve its perfimance
i heard about power filters is it improve my perfomance
what about the cost of it
some people says that power filters are not good for 100 cc bikes
and that make missing for my engine
plz help me

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avishkar May 10, 2010 at 12:16 pm

Hi,
wanted to wish u luck with the good work your doing for the bikers in India & i need ur expert advive for that. I’m planning to go for a BMC filter for my 180 Ug4. would that b good for my bike and what all changes r required. let me know and im not sure if ill b doing the upjetting for my carb coz i didnt do it for my previous bike with K&N 1060 and it is performing well. I changed the plugs to NGK iridium replaced the stock ones but didnt change the cable or the coils. but whenever i self start my bike it makes a wiered irritating noise dont no what it is . Can u advice me on that

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wilson June 5, 2010 at 2:01 am

I hav recently installed k and n air filter in mi fz16 without rejetting the carb. Actually i want to know do i have to change both main and pilot jet or only main jet and wat will b the best jet size to put be on nd how much will it cost…plz reply soon…..

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Srinivas.. October 20, 2010 at 12:43 pm

First of all i would like to thank DEEPAK for this blog which is giving so much knowledge about the bike tech’s… :)

Really the Efforts of Bikeadvice team is appreciable…!!!! :)

Abiram Menon,… A nice article…. Good work…!!! :)

So many of us want to know the info about Fitting a K&N Filter and Rejjeting a Carburetor…

the article gave a Very good info…!!!

I know about Lean and rich mixture but one new point i came to know was….

“When u closes the throttle in a downhill, if u hears popping or cracking sound from the exhaust, it is again due to the lean mixture.” :)

Another point Which was At Last But Was the Imp of all…..

“Manufacturers stick to a particular setting and not going for extreme tuning. Extreme tuning will call the need for extreme keeping up of it.”

This was again a brilliant point which makes all of our frnds to think about what they were going to do.. :)

Thanx to deepak once again.. :)

We were expecting more articles abiram.. :)

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Lionel November 6, 2010 at 1:28 pm

hello everyone,

I live in Pune own an Apache RTR 160 ,in which i have a K & N Rg 1060 filter.
i have tried getting it tuned at Bike Gurus Kothrud . He has told me that it is not necessary to rejet the carbs. But iam not convinced as I am sufering at the top end. It did 110 km/hr only.
Can anyone let me know:
1.what would be the correct size for the main jet required. Carb is Mikuni Bs 26.
2.where can i buy genuine jets in Pune or Mumbai ?
3.Is there any competent mechanic in Pune? Name and no?

Would be grateful for d info.

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naveen kumar December 29, 2010 at 2:46 pm

yea dere is da best mechanic i know..chinmay dangre…search him on facebook …he is with the name core power on fb…very talented knwledgable nd experienced.

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Samuel Fernandes December 8, 2010 at 11:01 pm

hey guys i really need to modify my classic 180 & i really need help from u guys
ny # 9920998988 please call and we can met up i stay in mumbai so any1 that can help me lets meet up and works on my bike to make it a power machine,would really like if you guys can help me i really wanna pump up my bikes power

looking forward to at leat a mail from you guys with tips on mods for my classic 180

thanks
Samuel

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naveen kumar December 29, 2010 at 2:43 pm

heyy experts..such an amazing article..i have many questions which i tnk u cn answer///….i am from new delhi..i have a pulsar 150..bought it in june 2010…3500 kilometers till nw…i want to get a k and n air filter installed in my bike..i love the sound it produces…i heard it a week back in my friend’s bike..he has yamaha fz16..da sound vas clean clear and roaring.but i have some questions
1.will the sound be good in my bike i.e. pulsar 150??by good i mean..respectibly loud,clean and clear…
2.i can compromise a bit with the mileage but not with the performance.my bike is new..does it adversely affects da bike if i get a k and n installed?
3.which filter to get installed??
4.i reside in new delhi..dont know any mechanic or performance modifiers who are well known bout jetting and everything..please give me da contacts for agood mechanic or shopin new delhi/
5. in the long run does it have any problem with the bike?

i have talked to a modifier who says normally jetting is not needed until da buike is showing problem after installation of filter..if it shows problem they will do jetting..
they are fitting the filter in the carburtetor…is it good?nd will da sound will be good?like aracing bike…please please please help…

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nikhil kapil January 12, 2011 at 5:33 pm

i have fz16 runs 24000kms i want install k&n filter in bike , i live in gurgaon , i dont know the place where to get the filter installed , wiil castrol bike center do this job properly , which k&n filter is best for fz16

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anupam January 23, 2011 at 7:56 pm

1st of all i’d lik 2 thank u for such a informative article.it waz very helpful.i;m not gud at technical stuff bt i’m havin a new pulsar 180 (1 yr old),i’ve fitted k & n filters n a bigger jet.but i’m not sure dat the jet size is proper.i’ve succesfully reachd da top speed of 124.plz suggest me da proper jet size for my pulsar.i’m also goin 2 fit ngk plugs.i’l be pleased 2 hear if u can also suggest me some mods 2 increase my byks tp speed..can u suggest any good mechanic n pune whu can do dis job well!..thank uu !n kip educating us!gr* job man!

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Pravin January 28, 2011 at 9:40 am

Guys plz tell me how can i improve my FZ-16 average?

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uday April 1, 2011 at 6:44 am

Fix the kandn filter for u r bike and NGK IR plug. Its Goes like any thing try it.
If u wanT more information contact me 9738612603

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Anto January 30, 2011 at 10:11 pm

Hi
I am planning to fit k&n filter for my 2005 pulsar 150 dtsi model. I reside in Coimbatore anyone know who fits these filters well in coimbatore. Plz reply as soon as possible. Reply me jennz55@gmail.com

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yuvaraj anand February 1, 2011 at 12:05 pm

Hey great article man! Well written indeed

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Renju March 1, 2011 at 5:30 pm

Dudes

I have purchased a K&N Air filter for my Yamaha FZ16. Now I need it to install in my bike. Can anyone please let me know where could I find a good mechanic in Kochi to do this?

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Josh March 20, 2011 at 3:07 am

hello i just want some help on some thing i have a yamaha rxs100 and want to put a K@N filter on it but im not sure on wot size to get?
main jet-120 -wot to upgrade it to?

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adarsh April 15, 2011 at 10:38 am

nice..and professional advice…thanks mite..one question..i am fittin pulsar 180old carb on a royal enfield 350 old which I am buildin..the bike seems to idlin with chock on but dies out so soon as I relese them..do I have to change any jets..if yes..pls suggest one which would fit it…thanks regards :)

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AJAX April 17, 2011 at 10:48 pm

How to fit K&N in FUEL INJECTED bikes (R15) ….???

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Martin May 17, 2011 at 8:50 pm

Hi guys Does anyone know ? I want to rejett the carb on my Tvs Apache 150 and I was wondering if anyone know what dimension i need to put, 120 130 140…. jet ? which will be compatible with the air filter (rc-1060 or rc-1100)?

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nitish April 18, 2011 at 3:23 pm

hey i own a pulsar 220f 2010 model… its already done 7000kms…i would like to know which airfilter i can install on my bike to increase power…?? and would it need re-jetting…???

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nitish April 18, 2011 at 3:26 pm

and guys please let me know if der are any good mechanics in bangalore who can help with re-jetting of the bikes and install airfilters…!!!

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kshitiz rawat May 14, 2011 at 9:24 pm

can a fuel injector be fitted on fz-s????

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C.M.MAHESH August 29, 2011 at 9:04 am

i have a karizma r the problem is i fitted the k&n air filter and the bike has hig pick up but the top speed has reduced to 110 and i just simply fitted the k&n air filter without any help of a mechanic

7n

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prithvi September 6, 2011 at 9:38 pm

i have 1 yr old 220, i got k & n fitted , awesome acceleration but top speed died down…please help…

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romy November 8, 2011 at 3:14 pm

HI
i have Royal Enfield Bullet Electra Twinspark and i want to fit a K&N air filter in my bull….. please let me know the K&N filter model and all other stuff need to be done like rejetting etc…
Is there any bad effect on the engine after altering the air filter??? or do the mileage drops down to a large extent as already its giving me the mileage of around 25 kms per litre???

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shaun November 9, 2011 at 4:14 pm

can u use a k and n air filter RC1100 in a pulsar 220 which has Fuel injector and not carboratter ???? will i have to do the jetting ????
pls reply at the earliest.thanks in advance.

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shaggy November 29, 2011 at 3:04 pm

would u recomend an k&n for my fz ???? will there b any change In mileage of t bike ??

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Alan Ray Samuel March 15, 2012 at 2:52 pm

heyy , i want to fit a k&n air filter in my fz , i would like to know if it reduces engine life ??.

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HISHAM KHALID May 19, 2012 at 8:31 pm

heyy..i want to upgrade my R15′s perfomnce…..i want to put an k&n ya-1208 filter..since it dsnt make much diffrenc on the bike except for grwling sound …. i hav heard about ECU REMAPPING ..how can i do that ..and what wil b the cost….i dont want to put daytona’s kit since it is way costly…….my budjet is somthing around 10k max…..

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jithin November 26, 2012 at 9:05 pm

Yay guys…anyone who hav planned to fix a power filtrr in ur fz16?then think twice…it has a misfiring problem in highr throttle positions…u can ask me doubt at jithuchand90@gmail.com….thanku..

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Rafshad March 26, 2013 at 3:31 pm

Hey guyz Im having a karizma r which has only done 1000 kms……i would like to install k& n filter on it…..which model of k&n should i install…?and what it costs…???
plz help me….totallly confused…..

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Adk April 16, 2013 at 10:38 pm

Hey….sir…i need your I have recently installed a k&n 1060 air filter im mu air box…..i want to know how to maximum performance from it…

Willl be waiting for your replu

Thankz in advance

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raju June 23, 2013 at 9:55 am

I want to install K&N air filter rc -1060 on my Yamaha r15 v.2 so please suggest what can I do with my bike …

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more detail about FZ16 carburater April 5, 2014 at 8:58 am

this was great post, I was in search of same post

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