Polaris 2001 High-Performance Snowmobile Service Manual (PN 9916690), Page 144Get this manual
CARBURETION Keihin Needle Explanation
Polaris currently uses Keihin PWK 39 carburetors on some of the domestic enginesWhat follows is an explanation of Keihin jet needle nomenclatureNOTE: Polaris carburetors are calibrated correctly for their intended useIt is not necessary to change needles for normal applicationsThe following is intended to be used as information to better understand the operation of Keihin carburetors and does not suggest that technician should be changing jet needles for any reasonThe only change for the needle that Polaris normally recommends is to the "clip" positionUse illustrations below and the explanation to determine the affect and characteristics of different jet needlesKeihin needles generally affect fuel delivery in three areas:
123The diameter (D) of the needle primarily controls fuel delivery from 18 to 14 throttle openingsA needle with smaller diameter at "D" would be richer than needle with larger diameter at "D" in the 18 to 14 throttle rangeThe length (L1) of the needle mainly affects fuel delivery from 14 to 12 throttle openingsA shorter needle will be richer and longer needle will be leanerThis produces same effect as raising or lowering the needle clip, but to larger degreeThe taper (A) primordially controls fuel delivery from 12 to 34 throttle openingsA steeper taper will deliver more fuel in this throttle position range