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Discussion Starter · #1 · (Edited)
Hey guys. I'm going to have to rejet my bike soon due to a lean condition. I figure since I'm going to rejet anyway, I'm thinking about putting in a k&n air filter in my bike.

I want to know mostly drawbacks of this modification. Past experiences are welcomed. Just to avoid a flurry of "what an aftermarket air filter does" googled answers, here are some of my questions:




-In what rpm range is most affected by a highflow filter, and how is it affected?

-What kind of gains are to be expected from a combination highflow filter and proper rejet?

-To what extent will engine life decay because of this modification?

-Would you do it to your bike?



Thank you for any intelligent answers.
 

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I have installed a K&N filter on my bike. I really didn't notice any real "seat of the pants" difference. The gains may be more with a rejet/exhaust upgrade. I would not think there would be a noticable difference in engine life.
The only problems I have run into with K&N filters is MAF contamination, which is not a problem on our bikes as we run carbs.
 

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Discussion Starter · #3 ·
Finally got around to rejetting my ninja. I recommend rejetting since ninjas come out of the factory lean, and lean out further with slip-ons, etc. I figure people may be able to use my settings as a good reference for what they might want to do with their bike.

Costs
If your planning on rejetting your ninja, seriously consider K&n filter pods. They cost about 60$ shipped and not only make your bike perform better, but made the rejetting job much easier. They get rid of the stock airbox which is a real pain to remove or put back in I would imagine.

The Dynojet kit cost about 90$ shipped which made the grand total for this 150$ for a more reliable, better running bike. After about 4 hours install time and more like 6 hours tuning time, I ended up with these settings:

DJ114 Main Jet
Needle Jet @ position 5 from top
Idle mixture screws 4 turns out


Benefits
It pulls so much better through the entire rpm range. Bike runs much better cold. There is no more gurgling at cruise between 5000-7000rpm. The spark plugs come out clean!! Also you get the peace of mind that you aren't roasting valves every time you accelerate.

But.....
Be prepared to do lots of fine tuning....i tried 3 different configurations before it came out right. The needle height & Idle mixture were the most tedious to work out, but both can be adjusted while the carb is still attached to the bike.

Also...
If I were reading this I would want to know that Factory Pro has a kit that comes with the filter pods and a better jet kit. That jet kit will have more main jets to choose from, rather than just the ones they recommend like the Dynojet. Its also nicer getting both the pods and the kit all at once so you aren't pulling your hair out because you have one and not the other.

Good Resources:
http://forums.ninja250.org/viewtopic.php?p=364005&sid=3e319a2f4a253f6bc8f654b98051f71a#364005
 

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another option is to use K&N 0990 air filter. It is a single filter.

http://www.knfilters.com/search/product.aspx?Prod=R-0990

Also when you remove the stock air box you will need to do something with the clean air system. With a header Just remove the whole thing .Block off the valve cover. OR the exhaust will POP when you down shift.
And a 5/8 filter on the bottom of the crankcase.
 
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