Mikuni TMX 35 needles explained

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ScooterLoopyJohn
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Sat Jan 17, 2009 9:09 am

This has helped me and i think should help all of you, complied by James Pennington (Australia).

Mikuni TMX35 needles
All TMX35 needles are of 6EN11 pattern.

6 signifies needles between 60mm and 70mm long (all 66.3mm long in this series)
E represents the total included angle of the first taper (1.25° or 1° 15’)
N represents the total included angle of the second taper (3.5° or 3° 30’)
11 is a “reference number”, relating to taper starting points (all the same in this series)

6EN11 needles are available in 7 sizes (52 to 58). The “working portion” of each needle comprises a straight section, a first taper section and a second taper section. The straight portion of the richest needle (52) is 2.52mm in diameter, whereas that of the next (53) is 2.53mm, making it a slightly leaner needle, and so on, until the leanest needle (58) at 2.58mm (a larger diameter needle passes less fuel, making the mixture leaner).

Each needle has 5 clip positions. Position 1 (top) is the leanest, while position 5 (bottom) is richest. Changing the needle clip by one position displaces the needle by 1.0mm.

Needles in the 6EN11 series are directly comparable. For example, the diameter at any point on a 6EN11-56 will always be 0.01mm larger than the diameter at that same point on a 6EN11-55. The starting point of each taper is the same on each needle.

On E taper, diameter changes by 0.02mm for every 1.0mm length
On N taper, diameter changes by 0.06mm for every 1.0mm length


Table 1 – Portions of needle in use, relative to clip position and throttle position (for all 6EN11 series needles)

Clip position Throttle closed ¼ throttle ½ throttle ¾ throttle Full throttle
1------------ S------------ S------------ E------------ N------------ N
2------------ S------------ E------------ E------------ N------------ N
3------------ S------------ E------------ E------------ N------------ N
4------------ S------------ E------------ E------------ N------------ N
5------------ S------------ E------------ N------------ N------------ N


S = Straight section
E = E (first) taper section
N = N (second) taper section

Even at full throttle, with the clip in position 5, approximately 5mm of needle remains in the needle jet. Thus, it appears that fuelling at full throttle is never dependent on the main jet alone.


Table 2 – Diameters of various needles, relative to clip position and throttle position


Needle Clip position-- Throttle closed-- 1/4 throttle-- 1/2 throttle-- 3/4 throttle-- Full throttle
6EN11-55 1------------ 2.55------------ 2.55------------ 2.34------------ 1.94------------ 1.41
----------- 2------------ 2.55------------ 2.51------------ 2.32------------ 1.88------------ 1.35
----------- 3------------ 2.55------------ 2.49------------ 2.30------------ 1.82------------ 1.29
----------- 4------------ 2.55------------ 2.47------------ 2.28------------ 1.76------------ 1.23
----------- 5------------ 2.55------------ 2.45------------ 2.24------------ 1.70------------ 1.17
6EN11-56 1------------ 2.56------------ 2.56------------ 2.35------------ 1.95------------ 1.42
----------- 2------------ 2.56------------ 2.52------------ 2.33------------ 1.89------------ 1.36
----------- 3------------ 2.56------------ 2.50------------ 2.31------------ 1.83------------ 1.30
----------- 4------------ 2.56------------ 2.48------------ 2.29------------ 1.77------------ 1.24
----------- 5------------ 2.56------------ 2.46------------ 2.25------------ 1.71------------ 1.18
6EN11-57 1------------ 2.57------------ 2.57------------ 2.36------------ 1.96------------ 1.43
----------- 2------------ 2.57------------ 2.53------------ 2.34------------ 1.90------------ 1.37
----------- 3------------ 2.57------------ 2.51------------ 2.32------------ 1.84------------ 1.31
----------- 4------------ 2.57------------ 2.49------------ 2.30------------ 1.78------------ 1.25
----------- 5------------ 2.57------------ 2.47------------ 2.26------------ 1.72------------ 1.19
6EN11-58 1------------ 2.58------------ 2.58------------ 2.37------------ 1.97------------ 1.44
----------- 2------------ 2.58------------ 2.54------------ 2.35------------ 1.91------------ 1.38
----------- 3------------ 2.58------------ 2.52------------ 2.33------------ 1.85------------ 1.32
----------- 4------------ 2.58------------ 2.50------------ 2.31------------ 1.79------------ 1.26
----------- 5------------ 2.58------------ 2.48------------ 2.27------------ 1.73------------ 1.20



Table 2 shows the needles most commonly used for Lambretta applications. Relevant dimensions of the other needles in this series (52 to 54) can be calculated using the information provided.

With reference to Table 2, it should be possible to adjust fuelling at specific throttle positions by changing the needle AND clip position in one go (and to predict the outcome based on the previous setting).
If changing the needle and/or clip position, do not change any other carburettor settings (main jet, pilot jet, air screw etc.) at the same time.

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drunkmunkey6969
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Sat Jan 17, 2009 10:31 am

Brilliant info, thanks for the contribution.

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