My very truncated notes on converting an Amal Concentric MK1 to premier spec.
Converting an old but unworn Concentric to Premier condition.
Revised removable pilot jet
1. Press out old pilot bush from the air screw side using a 2mm punch, the Pilot jet has a 2mm recess on this side and is 2.4mm overall diameter. Retrieve pilot bush and set to side.
2. From current blocked side using a 4mm drill drill out the new opening, stop when the drill comes to free air, then change to a 4mm end mill and make the hole a total of 0.825" or 20.95mm deep, the end mill creates a seat for the premier jet tapered tip to seal against.
3. Tap first 4mm section to 2BA, do not tap the second 4mm section or you will lose the jet tip seal.
4. Clean out and install Premier pilot jet.
It all hinges on centralising the first 4mm hole and being able to stay in that fixed position so best done on a vertical mill with DRO.
The old 25 pilot jet is a 17 thou hole so Amal use a 17 Premier pilot jet but the new routing appears to lean out the jet so the fix is to use a 19 Premier pilot jet.
Slide
Fit either an Amal Anodised slide or a Surrey Cycles brass slide with chrome plate.
Float
Fit the 'Stay up Float'
Float Needle
Amal fit an aluminum rubber tipped float jet.
I do mine on a Bridgeport Vertical mill with DRO using a 4mm milling cutter, this allows an accurate centering on the cast ring on the body. If you use a pillar drill then there is a greater risk of not getting the hole in the right position and the new premier pilot jet not sealing on the internal hole where the bush originally sat.