Im using a JRC PWK carb on my 1968 B44, the jetting is as follows:-
- main jet 130
- pilot jet 30
- needle clip position middle
- needle type JJM (straight section diameter 2.475, see http://www.allensperformance.com/data-n427-46.html
- air screw 1 1/2 turns out
When I originally installed the carb I found it was running rich. I eventually found that the needle was too narrow and fitted a JJM needle which has a thicker straight section and allows less fuel to bleed past the jet.
As received the JRC PWK didnt have any markings on the jets, so I swapped the jets for genuine Keihin PWK 28 jets which are readily available.
The JRC PWK carb is actually a clone of the Keihin PWK carb. What JRC engineering have done is to add a flange to allow the carb to be mounted on british bikes.
Im very happy with my JRC PWK carb and it does have some advantages over an AMAL Concentric
, such as a chromed flatside, a pullup choke enrichment device and a solid mounting flange which wont distort. Starting hot or cold is easy and performance is excellent.
The down side is that you may need to fiddle with the jetting. If your jets dont have any markings then I would replace them for genuine Keihin PWK jets. There are some good guides on tuning Keihin PWK carbs such as this one http://www.keihin-na.com/assets/1/7/slide_valve.pdf