Gas Needle Valve for Stuart 800 & Stuart Sandhurst

[BGH]

I would like to make a finely adjustable gas needle valve and would value some pointers as to the design. Its for a small gas engine, Stuart 800.
The mixer shown seems to work OK on another engine, even if its lacking in its visual refinement.
I need a fine thread, BA, BSB or ME no problem.
Now should the threaded brass part be bottoming out when screwed fully in, or more likely the needle itself??
In this example the needle is 1.8mm dia, so drill a hole that diameter with a standard drill bit ?, or should the tip of the needle seat into a matching tapered hole?
Should the needle have a longer taper? Ideal material for this?
Is this a good basic design, or are there published designs/ sketches available?
Any help gratefully received.

[pirmin]

hy, a sharp needle would do the trick, just like model aero engine carb needles i would say.

[BGH]

Thank you Pirmin, I will look into those .

[Jo]

A size 15 Darning needle will provide what you need.

Jo

[BGH]

Thank you Jo, I will look into those (-:

[Jasonb]

You can also rough out the taper on say a bit of 1/16" rod and then finish with a needle file. Put a bit of wood or MDF in the toolpost with a tapered Vee filed into it to support the delicate end.

Or if you want something a bit thicker turn the taper and make a reamer at the same topslide setting, these are for the fuel and burner on my Allman

[BGH]

Thank you Jason thats most helpfull.
Is there an o ring within the nut?
It looks neater without the spring (as on my example)
But think its the o ring in the Wade valves that causes fluctuation in the gas flow.

[Jasonb]

I just used a bit of Graphite Yarn gland packing.

[BGH]

Ah yes great, thank you! 😊👍

[Jasonb]

Section for you. It also makes the needle captive so no chance of screwing it out too far and making a flame thrower.

[BGH]

Great thank you, well that explains some more of the mystery, at least in my head! 😅
I suspect I will try the simple option first but may come back to this if I want to refine it.
That's all a great help, much appreciated 😊👍

[BGH]

A quick update on the needle valve project..well its stalled, for now.
I bought some darning needles as suggested by Jo, but have progressed no further. The engine stopped when I stepped outside to hear how loud or not it was, and has not run again since.
Its currently got me stumped and I am waiting on some expert in person help to try and locate the issue. I know its lost all compression but cannot locate why. With the gas hose removed air from the cylinder is being pushed out of the gas inlet when I turn the engine over by hand. The timing I don't see as being out as everything is keyed in place. Ive had the valve chest off and ground in the gas and air valve. However I cannot see that its the valves that are leaking if I follow the possible path of the gas.
I have just bought a Stuart Sandhurst, so will need a needle valve for that and also the air intake section. So no doubt I shall be back here in due course in the hope of more expert help!
Cheers Chris.

[Jo]

Good Luck, it should be possible to find the leak.

The Sandhurst uses a standard Amal carb.

Jo

[GRAUBELE]

This is the carburetor of my STUART Sandhurst.

Dieter


Edit: Supplemented with picture of Lucas SR Magneto.

[Jo]

That is very pretty 

Jo