The spigot on the bottom of the carburettor takes a non-return valve that sits just off the bottom of the fuel tank. This is a fairly simple turning/milling job from a piece of brass stock. I started by turning down one end of some bar to 8mm dia and threading M8 x 1; then drilled a cavity for the ball that acts as the valve, then I milled a 10mm AF hex.

Now holding by the 8mm diameter the other end was turned and tapped so it could be screwed into the carb body and a small hole drilled to receive the end of the needle.

The cap that goes onto the end of the M8 thread to retain the ball was turned and bored with a generous undercut to ensure the threads screwed all the way home.

The final part was the needle which was turned, threaded and knurled from some 303 stainless.

This pic shows the three parts and all the tools that were used in their making though there is one die missing.

Rather than trawl the supermarket or tobacconists shelves for a suitable flat round tin to use as a fuel tank I decided to make mine from scratch as I wanted the sides to have that bead rolled look that you often see on round sheet metal containers.

I started by cutting a slice off some 3" x 16g copper tube that I had and then turned a piece of MDF so that the tube was a tight push fit onto that so the ends could be finish turned. Then using a sharp DCGT insert the OD was reduced to leave two flat bands that were then rounded off by hand to represent the bead rolls.

A piece of 1.5mm brass sheet was sandwiched between two pieces of MDF and turned to diameter once the corners had been sawn off. I then  turned a 0.5mm tall spigot to a tight fit into the pipe. Having the pipe in place on the tailstock makes it easy to test fit without having to keep retracting the tailstock support. The remaining 1mm thick edge was rounded over with a file.

The four mounting holes were then drilled and used to make sure the work stayed put while the external shape was milled to incorporate the four mounting lugs.

The top was drilled centrally to clear the hexagon of the non return valve, Drilled and tapped for four screws to hold the carb body using the recorded DRO readings from when that was machined and finally a hole off to one side for the filler neck.

The parts could then all be soft soldered together, here is the finished tank complete with vented cap and the carb body in place.

PART ONE  TWO  THREE  FOUR  FIVE  SIX