Saturday, December 3, 2011

Wall Autowheel carburettor

Post World War One Wall advert.

I'm well aware that my blog is at the best of times one of very narrow interest. In this post however I seek to narrow it down yet further to a level of obscurantism beneath which it would be hard to sink...

The Wall Autowheel has an interesting story involving backing by Sir Arthur Conan Doyle and mechanical insporation from the wonderful FN four. However ladies and gentlemen I shall brush over all of this and go straight on to the fascinating subject of the Wall Autowheel's carburettor.

I will start with the let down that I don't even know who made the carb. This posting is just some technical info for a fellow Wall owner. As I was going to write it down anyway I thought I might as well post it online on the narrow offchance that it may help someone else at some distant point in the future.

Wall Autowheel carburettor.
The carb is of extremely simple design. There is no slide needle and air adjustment must be set in advance with a clip set on the top of the carb body just beneath the top bezel. So far I've run mine with the air fully open and not experimented with other settings but as mine does run hot perhaps on the next outing I'll close the air a little and enrichen the mixture (mine runs on a very weak two stroke mix for extra lubrication).

Wall Autowheel float needle.

Firstly, my measurements are relatively accurate (from a limit gauge) but not absolute. Bear in mind too that the parts are nearly 100 years old and have already had a full life so are perhaps not quite to the designer's blueprint, if any components fitted indeed ever were in the first place.

The float needle is 2 11/32" long. A spring clip holds the needle in place. The needle has 13 notches acting as positions for the clip to adjust the height of the float. The notches begin 11/16" from the top of the needle and are spread over 5/16". I run mine with the bottom of the clip on the top notch. This gives roughly 1/4" of movement on the float between fully closed and fully open.

Wall Autowheel float needle clip. 

Wall Autowheel carb dismantled.

Wall Autowheel carb front side view.

The above view of the carb clearly shows the air adjustment clip.

Right, now I can sit back and see my page hits go through the roof!


  1. Richard: Thanks very much for this carb post.

    The information and photos are very useful indeed. Your float needle is very different from mine. Mine has a brass oversleeve instead of grooves. I guess this sleeve is soldered in place and can be moved by melting the solder. I will need to make up my own clip to go above the float.

    The 1/4 inch of total float movement that you describe gives me a very good guide for setting my float height. I presume that means that the bottom of the float is 1/4" above the base of the the float chamber.

    By the way, have you ever re greased your exhaust cam? I have been lead to believe that the cam and the bearings get no engine oil and depend on grease which is supposed to be 'topped up' every 2 or 300 miles. It looks to me that this requires at least a partial engine strip. Have you ever done this job? If so another blog on cam greasing would be brilliant! Maybe you should think of writing a WAW owners guide!

    Thanks again for the carb info. I'm off to the garage to do some work on my bike now.


    Pete P.

  2. Richard: By the way, do you know if the type of float needle that you have in your carb is available to buy anywhere? I very much doubt it but I thought I should ask!


    Pete P.

  3. Hi Pete, Happy to be of help with the info. Sorry for taking a while to get back to you. Have been away from the internet for a while! Hmmm.. I would think chances of finding a spare float needle are pretty low. Best bet may be to contact Martyn Bratby - he seems to have quite a few spares for vintage carbs and it could be that something else would fit or modify easily. Yes the bottom of the float is 1/4" from the bottom of the chamber when full of petrol. Never heard about greasing the exhaust cam. I'll have a look into it! May take a while though as I work away from home and it'll be more than a month till I'm back. In the meantime Merry Christmas and all the best for the New Year.

  4. Thanks for the pointer - I'll give Martyn a buzz and see if he can help. I will also see if I can find out a bit more about the exhaust cam greasing myself and I'll let you know if I come up with anything.

    I hope you too have a very enjoyable festive break.

  5. I've started a new Facebook Wall Autowheel group if you are interested: