Part 25 By Vince Cutajar

Before continuing work on the carb body I needed to do the banjo connector and the fuel jet housing. These would determine how much more milling was needed on the carb body.

I fabricated the banjo connector from two pieces of brass. First I did the circular part which was simple work on the lathe. Then I did the straight part on the lathe but drilled the through hole 0.5mm undersize (2mm).

Put the circular part in the vice and plunge drilled with a 5mm slot drill. I did not go all the way through the banjo. Applied some solder cream at the bottom on the plunged hole. Pressed in the other part of the banjo and applied heat to the part. I then started threading 6 x 0.75mm. I then drilled the hole for the banjo 2.5mm which cleaned up the solder that might have gone in the hole.

Next, started work on the fuel jet body for the carb. Machined the front part of the jet on the lathe and then drilled the jet hole 0.7mm.
I noticed that the plans have some missing dimensions for the jet so I guessimated some things.

First off I needed to make a 1/16" groove where the banjo will sit. So I used a 2.5mm drill which had the backside ground to a point to use as a transfer punch, put the banjo in the jet housing, and with this transfer punch scratched the housing where the groove should be.

I then cut the groove  but the plans do not specify how deep the groove should be, so I made it to a depth of 0.75mm.

Then I drilled some 1.5mm holes in the groove. The plans do not specify how many so I drilled four.
Working on the back part of the jet, I used a collet holder instead of the 3 jaw chuck. Machined and threaded the back part 6mm fine. Then drilled, counterbored, countersunk and tapped 3mm the inside of the jet making sure the thread reaches the banjo groove.
Managed to drill and tap the carb body for the jet assembly.

Inserted a 5mm rod in the carb air inlet and used this rod to measure the angle. Then drilled and tapped and milled the platform where the banjo will sit. This operation was done repeatedly in small increments until the tip of the jet just appeared in the carb air passage.showing the jet assembly screwed into the carb body. Left the carb in the vice so that next time I could mill out the small defect in the casting that is evident in photo.

Drilled the carb primary air passage (1.6mm).
Started work on the jet needle valve. Instead of doing it in one piece I decided to do it in two pieces; the needle shaft and the knurled knob. First attempt at machining the needle shaft ended in a total failure but the second attempt was a success.
Started with a stainless steel 3mm rod and turned the needle taper (10 deg inclusive).
Then I needed to reduce the 3mm shaft to 1.2mm and that is where everything went wrong on the first attempt. Second attempt was done by grinding the shaft instead of turning it. Unfortunately I do not have a toolpost grinder so a Dremel was clamped to the toolpost A cutting disk was used for grinding. This method was successful.
Next the shaft was threaded 3mm. Length of the thread was done by trial and error as no dimensions were specified on the plans.
I finished the knurled knob for the needle shaft and I superglued the needle shaft to the knob.
So now all the major parts of the engine are complete.
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