Part 24 By Vince Cutajar

What was previously used as a mandrel was parted off and finished as the throttle body. A shallow slot was milled to accommodate the handle. This is not in the plans but I thought I would do it to give more support to the handle.

Next a thin (2mm) disk was parted off from the same material as the throttle body . This was further machined to make the handle.
Using the casting chucking stub, the body of the carb was chucked up trying to keep the centre of the bore in the middle as much as possible. First both sides of the carb mounting flange were faced off.

Next the drilling operation of the carb bore had to be done but before that a big decision had to be taken. Westbury states that if should be a maximum of 0.25" (6.35mm) diameter but then he says that for moderate speed and maximum flexibility in control, the bore can be reduced to 3/16" (4.76mm).

So I decided to do the bore 5mm. With the throttle body fixed in place, drilled and reamed for 5mm but did not go all the way to the chucking stub. I did not want to decrease the strength of the stub for the next machining operation. Using the previously made taper D-bit the venturi of the carb was machined . As can be seen in the photo a piece of the D-bit chipped off. I guess it was too hard. Also a sizable burr was produced on the casting. This was cleaned up and then the rest of the 5mm bore was drilled and reamed.

The carb was fitted on a mandrel and lightly tapped on with a plastic hammer. I hoped I could remove it later on.
Using a live centre the inlet O.D. was machined. Then changing to a half dead centre the face of the inlet was machined.
Now to give the carb inlet the bell mouth shape. Using a centre drill the inlet was opened up. Next a countersink bit was used and this was used to half the depth of the previous operation. Then using a half round needle file the bell mouth shape was formed to a 12.5mm radius, sand paper and polishing giving the final result.
Drilled the two mounting holes on the carb flange using the flange brass template I had used on the cylinder head. The mounting flange was cleaned up and filed down to size. While I was at it I decided to clean up the whole of the carb body.
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