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Ninja 250 Carburetor Needle Information: Difference between revisions

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=Background=
=Background=


The needle in a carburetor is the main method of adjusting the mixture
The needle in a carburetor is the main method of adjusting the mixture at partial throttle openings.  It blocks some of the passageway to the main jet (the main jet size determines the carb's overall mixture), reducing the amount of fuel allowed to flow at part throttle.  This keeps the mixture consistent through a range of throttle openings: as the throttle opens, raising the slide, the needle also raises (it's attached to the slide). The needle has a tapered profile, so that as it pulls out of the main jet port, it blocks less and less of the port, allowing more fuel to flow, ideally matching the amount of air flowing through the carburetor.  By the time the carburetor is at full/wide-open throttle, the needle is completely clear of the main jet port, allowing it to flow without restriction.
at partial throttle openings.  It blocks some of the passageway to the main
jet, reducing the amount of fuel which is able to flow during
partial-throttle operation, thus leaning the mixture.  As the slide
raises, the needle is pulled further out, until at full throttle, it's
completely clear of the jet, allowing the full amount of fuel to flow.
The needle is tapered, so that as it's pulled further out of the main
jet, it blocks less of the port, and more fuel is allowed to flow.


The rate and positions at which the needle tapers, along with the
The rate and positions at which the needle tapers, along with the
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the engine, correspondingly more fuel is drawn in as well.
the engine, correspondingly more fuel is drawn in as well.


Needles only really have one adjustment: height.  As you raise a needle
A given needle only really has one adjustment: height.  As you raise a needle
(by moving the clip lower on the needle, or adding washers), you enrich
(by moving the clip lower on the needle, or adding washers), you enrich
the mixture.  As you lower a needle, you lean the mixture out, all at
the mixture.  As you lower a needle, you lean the mixture out, all at
partial throttle.
partial throttle.


Another adjustment you can make with needles is to replace them with a
You can also "adjust" the needle by substituting different-profile needles for the stock units.  There are practically two ways to
different needle, which has a different profile.  There are two ways to
do this: you can purchase a jet kit, or you can try needles from other carburetors.  Enterprising riders with machining skills may also manufacture their own needles on a lathe, but this is beyond the scope of this article.
do this with pre-made needles: you can purchase a jet kit, or you can
try needles from other carburetors.


The Factory Pro and DynoJet jet kits provide clip-adjustable needles,
The Factory Pro and DynoJet "jet kits" provide clip-adjustable needles,
and are misnamed: they're really a set of custom-made needles, with
and are misnamed: they're really a set of custom-made needles (into which FP or DJ has put a lot of work and research), with
some jets thrown in very nearly as an afterthought.  They should be
some jets thrown in very nearly as an afterthought.  They should be
called needle kits.
called needle kits.
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==Stock==
==Stock==


The stock needle in a Ninja 250 is known to have a very lean midrange,
The stock needle in a pre-08 Ninja 250 (this article doesn't specifically pertain to 08+ bikes) is known to have a very lean midrange,
and a relatively rich top end.  This is because the EPA performs its
and a relatively rich top end.  This is because the EPA performs its
emmission testing at midrange, and the manufacturer wants to have the
emmission testing at midrange, and the manufacturer wants to have the
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Reprofiling a stock needle is a job for a machinist, and is beyond the
Reprofiling a stock needle is a job for a machinist, and is beyond the
capabilities of most Ninja 250 owners.
capabilities of most Ninja 250 owners.
The Ninja 250's stock carburetor is a Keihin CVK30.


The stock needle is marked N16I at the top, and is Kawasaki part number 16009-1461.  It's made of brass.
The stock needle is marked N16I at the top, and is Kawasaki part number 16009-1461.  It's made of brass.
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mm thick, so that the needle can be adjusted in about half-millimeter
mm thick, so that the needle can be adjusted in about half-millimeter
increments.
increments.
==DynoJet==
[[File:jetneedle-horiz.jpg|right]]
BrianM submitted this information about an aftermarket jet needle.  He was unsure which needle it was, but as the measurements don't match those of the Factory Pro needle above, it's likely that this is the DynoJet needle.
<table border=0>
<tr>
<th> Diameter/Taper </th>
<th> Length </th>
<th> Colored line </th>
</tr>
<tr>
<td> 2.44mm diameter </td>
<td> Unknown </td>
<td> To black line </td>
</tr>
<tr>
<td> 2.44 - 1.92 mm taper </td>
<td> 15.47 mm </td>
<td> Black to blue line </td>
</tr>
<tr>
<td> 1.92 - 1.11 mm taper </td>
<td> 2.5 mm </td>
<td> Blue to yellow line </td>
</tr>
<tr>
<td> 1.11 mm diameter </td>
<td> 13.18 mm </td>
<td> Yellow to red line </td>
</tr>
</table>
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