Atco Standard 16 Renovation - Carburettor

Five months ago I wrote about this renovation asking if anyone had the dimensions of the missing float needle. My carburettor is the early Atco model for the smaller engines, you can see it is missing as it should protrude through the hole in the centre of the float chamber cap. From pictures I have seen I think it likely that many of the float chamber parts are common to the Senspray model.

I’ve now been able to purchase a complete carburettor and below is a picture of the float, needle, clip and a brass ring which I found beneath the float. Jarrett posted back in April 2017 that he found a similar ring in his float chamber and there was one in my original carb so there is no doubt that it should be there, but why? My only thought is that when the float chamber is empty then without this support the float would sit on the base of the chamber and possibly restrict the flow of fuel from the bottom feed. Not very convincing I agree but does anyone have a more likely explanation?

Interestingly, with this ring beneath the float there is very little movement available; between the high and low positions the vertical movement is only about 3mm.

I can imagine I’m not the first person to need a float needle. If the needle is not properly secured with the clip it can drop out of the bottom of the float chamber when the fuel pipe fitting is removed.

For anyone needing one I have taken the dimensions. The needle is 69mm long and the main body is 2.3mm in diameter (perhaps 3/32”). The slot for the clip is 24.3mm from the top of the needle and 43.5mm from the bottom (the slot is approx. 1mm wide). The float itself has a diameter of 36.3mm and an overall height of 31.9mm, and has a slightly convex top and bottom.

Before buying this second carburettor I felt it likely that a float needle from an Amal motorcycle carburettor might be suitable and now having the correct needle I’m even more certain. The float needle for a No. 1 size float bowl, Amal part 14/024, would be suitable except that it is slightly longer and would need a new slot for the clip at the correct position (based on the dimensions above). A suitable clip would be Amal part 4/230. Both parts are available from various sources (e.g. https://www.hitchcocksmotorcycles.com/partsbook-pages/3379 parts 12 & 42).