Modification Intentions - Kawasaki Ninja 250R Forum
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post #1 of 11 (permalink) Old 05-17-2013, 10:07 AM Thread Starter
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Modification Intentions

Ok, after painful reearch I have approached a conclusion/decision regarding performance enhancements for my new little girl.

I propose to replace the stock 14t/45t sprockets with a 14t/47t and new chain to accomodate the new length requirement. All for the purpose of providing more torque at the wheels while sacrificing top-end speed. I don't really "cruise" on this little thing because if I wanted to Cruise I would have bought a cruiser...

I am also considering the Yoshimura slip-on exhaust and the then requisite jetting adjustment along with an aftermarket air filter of the UNI type or K&N

Whatcha Think
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post #2 of 11 (permalink) Old 05-17-2013, 10:23 AM Thread Starter
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Also....

What is the OEM Chain Size? 520?
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post #3 of 11 (permalink) Old 05-17-2013, 10:24 AM Thread Starter
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tooth config change

I mis-typed earlier, I mean to go to a 13t/47t setup.
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post #4 of 11 (permalink) Old 05-17-2013, 10:50 AM Thread Starter
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yet another question

So, If I install a slip-on exhaust and a UNI air filter, what type of "carb tuning" will be needed? turning carbeurator adjustments? or perhaps even replacing different jet sizes?
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post #5 of 11 (permalink) Old 05-17-2013, 02:42 PM
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More air flow will require carb tuning.. Replace the jets with dynojet kit since the stock setup will run too lean with slip on and air filter upgrades. It'll run like shit actually.. Even with stock setup, dynojet makes a huge difference. Highly recommend..

2014 Kawasaki Ninja ZX6R 636
2001 Yamaha YZ426F dirtbike
2012 Kawasaki Ninja 250R
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post #6 of 11 (permalink) Old 05-18-2013, 03:28 AM Thread Starter
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Thanks AZ!


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post #7 of 11 (permalink) Old 05-18-2013, 05:57 AM
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Quote:
Originally Posted by hntr2k View Post

Whatcha Think?
With the gear ratio you're proposing and since you don't cruise, I take it you plan to stunt the bike?

A 13 tooth front sprocket will rub the chain guide and the low end torque gain you expect will not be all that great, even with a 3-4 HP increase. most torque increases show up in the higher rpm range depending on the tune.
No need for a new length chain. There is only a .21 inch distance difference between sprockets (stock 14/45 compared to 13/47).

If you remove the airbox and install the pod type filters, you will need to install larger main jets. In fact the best tune you'll get on pods will be worse than the best tune you'll get with a box. If you want more flow, take out the snorkel... use a higher flow air filter (drop in type), but keep the airbox. The airbox smooths the air flow giving you the potential for more power vs a pod filter. The exact same or similar results you get with pods you can get with the stock airbox and full exhaust system. This has been proven on the dyno. Shim if you want to use a slip on.


Here's some good info to read.

Motorcycle Carburetor Theory 101
http://www.motorcyclecarbs.com/carbs101.pdf

Resonant Airboxes: Theory and Applications

Pipe Jetting (A Must Read)
http://www.motorcycleproject.com/mot...s-jetting.html
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post #8 of 11 (permalink) Old 05-18-2013, 02:07 PM
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If you want such a huge difference in gearing go with a larger rear sprocket. The smaller you go.in front wears chain out faster. I ran 14/48 (-2+5) on a gsxr once and it was a huge difference. Top speed was around 125. Normally 165. But it pulled something serious. Lol. Maybe go only one down in front and four up in rear. It already has low gears you wouldn't want to make it worse. Just my two cents.

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post #9 of 11 (permalink) Old 05-18-2013, 07:40 PM Thread Starter
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Thank you very much for the conversation and advice. I am being told locally by a mechanic that a "typical" sprocket modification is a "one down (f) two up (r)". I thought that would leave the resultant number at 13/47 which I was told would not be quite "stunt" dramatic, but would pull much more low-end torque for quick, local riding. I have not discussed the front sprocket change causing a chain guide rub with him yet.

About the air, get a drop-in high flow filter (keep the air box), full exhaust, and jet kit the carb? Is that right?


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post #10 of 11 (permalink) Old 05-19-2013, 08:21 AM
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Quote:
Originally Posted by hntr2k View Post
Thank you very much for the conversation and advice. I am being told locally by a mechanic that a "typical" sprocket modification is a "one down (f) two up (r)". I thought that would leave the resultant number at 13/47 which I was told would not be quite "stunt" dramatic, but would pull much more low-end torque for quick, local riding. I have not discussed the front sprocket change causing a chain guide rub with him yet.

About the air, get a drop-in high flow filter (keep the air box), full exhaust, and jet kit the carb? Is that right?

Yes the "typical" sprocket mod to get the bike to exhibit more torque is to go down 1 tooth on the front and up 2-3 on the rear sprocket. Also the "typical" bike this is done on already has a ton of HP and torque to begin with and comes stock with either a 15 or 16 tooth front sprocket.

The Ninja 250 is not the typical bike as it neither has very much HP, torque or a stock 15 tooth front sprocket. That is why during your research you probably did not find too much about a 13 tooth front sprocket, but a lot about a 15 tooth. If you really think about it, the Ninja 250 is already geared too low (under geared). It actually (wastes) does not utilize the HP it has to it's full potential. Gearing down any further, not only will you lose top end speed but some in between. What you will get is an engine that's revving crazy high, with a slight bit of pull in 1st gear that's going nowhere. Use Gearing Commander to help you figure out your gearing.

With a good drop in filter like the Pipercross or Hurricane, a full exhaust and jet kit, you'll get a slight increase in HP and torque on the low end. For that fact even shimming the needles will help with a better throttle response.

The key is finding out were your power comes on. 1/4 throttle (3k rpm) is where you really start to see more fuel added to the mix. This is also a good launch speed. The Ninja 250 is never going to be a bike that has any significant amount of low end torque.

Last edited by DaBlue1; 05-19-2013 at 08:40 AM.
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