Snowmobile Polaris High Performance (2001 year). Manual - part 36
CARBURETION
3.19
Keihin Needle Explanation
Polaris currently uses Keihin PWK 39 carburetors on some of the domestic engines. What follows is an explanation of Keihin
jet needle nomenclature.
NOTE: Polaris carburetors are calibrated correctly for their intended use. It is not necessary to change needles for normal
applications. The following is intended to be used as information to better understand the operation of Keihin carburetors and
does not suggest that a technician should be changing jet needles for any reason. The only change for the needle that Polaris
normally recommends is to the “clip” position.
Use illustrations below and the explanation to determine the affect and characteristics of different jet needles.
Keihin needles generally affect fuel delivery in three areas:
1.
The diameter (D) of the needle primarily controls fuel delivery from 1/8 to 1/4 throttle openings. A needle with a smaller diameter at
“D” would be richer than a needle with a larger diameter at “D” in the 1/8 to 1/4 throttle range.
2.
The length (L1) of the needle mainly affects fuel delivery from 1/4 to 1/2 throttle openings. A shorter needle will be richer and a longer
needle will be leaner. This produces same effect as raising or lowering the needle clip, but to a larger degree.
3.
The taper (A) primordially controls fuel delivery from 1/2 to 3/4 throttle openings. A steeper taper will deliver more fuel in this throttle
position range.
Taper “A”
L1 and Clip Position
Diameter @ “D”
Throttle Opening
0
1/8
1/4
1/2
3/4 Full
“A”
“D”
“L1”
2.515mm
Ill. 1
EXAMPLE: R--1370G
R--1370G
R--1370G
R--1370G
R = Aluminum Construction
13 = Taper Angle of the needle (depicted at point “A”)
13= 1
34’ a 14 would be 1
45’
The larger the number = the steeper the taper.
A steeper taper is richer than a shallow taper.
An R--1470G needle would be richer in the 1/2 to 3/4
throttle range than a R--1370G needle.
70 = Diameter of the straight portion of the needle (see
point “D”).
A larger diameter needle at point “D” would be
leaner in the 1/8 to 1/4 throttle range than a needle
with a smaller diameter at point “D”.
A R--1368G has a diameter of 2.685mm at point “D”
A R--1370G has a diameter of 2.705mm at point “D”
G = The length from the top of the needle to a point on the
taper that is 2.515mm in diameter.
A “G” is shorter than a “J”.
This length mainly affects mixture in the 1/4 to 1/2
throttle range.
A R--1370G is shorter at “L1” than a R--1370J and
a R--1370G is richer in the 1/4 to 1/2 throttle range
than a R--1370J.