Amal 930 to premier spec?

Yes, I do it on a vertical mill, I have the depth data somewhere.

To prepare the carb I drill and tap the opposite side to the mixture screw 2BA, the pilot bush is exposed and then I knock it out from the mixture screw side and out the freshly drilled and tapped hole. After a good clean and a bath in the ultrasonic cleaner the premier pilot jet can be screwed in, the chamfered tip fits into the hole left by the pilot bush. 30 old pilot jet is the same size as the new 19 premier pilot. 

I do the change to improve access to the pilot jet, if the carb was giving idle issues before then I would only convert the carb after getting it to run right with the pilot bush.

Have you cleaned out the pilot bush with a 16 thou drill, prodding with wires and fluids will not clean it properly. Worn slides also give variable idle as they rattle about leaking varying amounts of air.

- variable jet inserted, 

The pilot bush and jets are fixed sizes and meter the fuel to a fixed rate set by the size. If clogged that rate is reduced out of tolerance for the air mixture screw to cope.

- the left hand tapered needle inserted. (What is the intention with this?)

This is the air mixture screw and meters the air, with the right sized and clean pilot jet the proper idle mixture will be from 1.25 to 1.75 turns out from closed, hence the initial starting point of 1.5 turns out before tuning.

Read this webpage for more detail.

http://www.jba.bc.ca/Bushmans%20Carb%20Tuning.html

Where are you getting this variable jet idea from, you can change the jets to different sizes but once in place they are fixed to the size they are stamped. You vary the mixture by the air mixture screw which adds or reduces air to the fixed amount of fuel. The new premier pilot jet is the same, no air just fuel.

If you want to try the 2 stroke pilot position then first you drill the 4 stroke pilot bush oversize to remove it's metering, then you can add the 2 stroke pilot to the pre drilled hole under the carb.

Removing the pilot bush can be a pain, drilling it with a 2mm drill will remove its influence and leave the 2 stroke pilot jets as the fuel restriction. Note that the first concentrics all had the pilot jet in the 2 stroke position but after a year or 2 the issues that position gave on 4 stokes were overcame by the pilot bush which then were made standard for all 4 strokes. You may be adding more problems not less. What are the issues you have with the idle on the bike.