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Tuning the Needle in your carb

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  • Tuning the Needle in your carb

    Cut and Copy from somewhere else for our benefit:

    Understanding Keihin needle codes. By Pobit

    what is the difference between an N3CJ, and N8RF ? (leaner or richer?)

    The tapers are the same on both needles. Only the length measured from the top to where the taper is located and straight section diameter differ.
    The third letter determines where the tapers are located and their relation to the clip grooves.
    Line the tapers up and the clip position looks like this: N3C_#3 = N3E_#2.5 = N8R_#2.
    The last letter denotes the straight section diameter. From rich to lean: E,F,G,H,I or W, J, K. These needles have a fairly lean end taper.

    The next most common OEM Keihin needle used for two strokes is the NOZ_ and N1E_ series needle. These two needles have the same tapers and differ only by length. NOZ_#3 = N1E_ #2.5. Straight section diameter code is the same as the above needles.
    The length code is not the same between different series needles so no direct comparison can be made. These letters can only be used to reference clip position placement within the same series. What that means is you can't assume switching from a N3EH in the #3 clip will be the same starting point as a N1EH#3 even though they both have an E in the third position. This series needle is known for its rich end taper.

    We may as well include the JD needles and Sudco needles in this comparison too. If you line these needles up by where the first taper starts with the same straight section diameter and clip position, it looks like this:
    JD blue = DDK = N3EE
    JD red = DDN = N3EH

    This is not exact as the tapers and diameters don't line up perfectly but is very close.

    The JD red and blue needles are identical in tapers, length and clip position. Only the straight section diameter differs. These needles are similar to the N3E_ needles but have a richer end taper.

    All the above needles are multi tapered needles except the Sudco needles which are straight tapers.
    The first letter in the Sudco needle code is the taper angle. The two most commonly used taper angles are C and D. The D needles have a steeper taper so they get progressively richer towards the end of the needle compared to the C needles.
    The second letter is the length of the needle which can be used to reference clip position. The third letter denotes straight section diameter. The link is to a graph of Sudco needles and makes it easy to understand their needle codes. Sudco Needle Chart
    Last edited by Jon Mutiger; March 26th, 2010, 07:31 AM.