Jet Needle KEIHIN JJK
for KEIHIN PWK 28
Together with the mixer tube the jet needle regulates the composition of the mix in the partial load or half throttle ranges. The needles differ in terms of their colour, pattern, internal coating and dimensions. Each of the ranges has a specific effect on the composition of the mix. As a rule, the following applies: The bigger the jet, the richer the mix that results. The bigger the needle, the earlier the mix is enriched.
The needle also has various clip positions, with which it is possible to determine its position. The higher the clip snaps into place on the needle, the deeper it is immersed in the mixer tube and the leaner the mix is in the half throttle range. If the needle is already in the lowest position and mix is already too rich (evident for instance if the Vespa sounds like a 4-stroke scooter when its slide is half open), then you should choose a thicker needle or a smaller mixer tube.
Conclusion: In this case, patient testing pays off as the carburettor can only work perfectly with a suitable needle.
SIP-TIP: Needle clips are often lost. The best idea is to order the replacement clip (part no P3420104) at the same time.
OEM Numbers (for the purpose of comparison)
46-JJK PWK J/N (KEIHIN)