Bates and Edmonds Bull Dog restoration, Part 4

A Bull Dog gets its bite back

| May 2009


Editor’s note: The following is Part 4 of a four-part series on Peter Rooke’s restoration of a 1-1/2 HP Bates & Edmonds Bull Dog.

Fuel Mixer
All that remained of the original fuel mixer was a broken rusty stub in the cylinder head. I had been able to take some external measurements to go with some photographs that had been taken of a friend’s mixer.

The first item that I needed was a cast pipe fitting that could be adapted for the bend and mounting to the cylinder head, part of which was cut off to get the right profile. To make it easier to machine the mixer, the main body would be fabricated from six pieces of steel!

A 2.5-inch length of 1-inch internal diameter iron tube was turned to match the smaller diameter of the pipe bend and then bored out smooth. The venturi was then machined from a 2.625-inch length of solid steel, a 0.500-inch hole first drilled through the length of the steel before cutting a taper in both ends, leaving approximately 0.750 inch in the center as 0.500 inch outside diameter for the constriction.

The diameter of the venturi piece was reduced to fit inside the tube leaving 0.125 inch protruding to fit into the end of the pipe bend in order to provide a locating lug when brazing together.
A piece of 2-inch diameter steel was machined next to form the outside of the bell mouth at the bottom of the mixer, cutting a parallel taper inside.

The bell mouth, center tubes and venturi were the first components to be brazed together and were then cleaned up. This part of the assembly was then put on the lathe and the internal tapers tidied up, to ensure a smooth surface with no ridges to interrupt air flow. At the same time the shoulder was cut to take the fixed part of the choke plate.