Vintage Workshop
Services for Brough Superior motorcycles and their contemporaries

AMAL carburettor Twin Float Chambers

7/2005: I had helped out a friend in England with pictures and sketches of the twin float chambers used on Brough and Morgan AMAL carbs.

Now Ian has some experience with lost wax castings, but anyway I was quite surprised when he came up with this pic only a few months later!

Ian, I hope you don't mind my showing two of your pictures::

This is the mould for casting on of the wax prints...

... and these are the prints.

If you are interested in a set of unmachined castings, drop a line to Ian, and give him my best regards. He asks 45 GBP for a twin float set, i.e. bottom bit, 2 bowls and 2 lids, which I think is very good value for money!

Ian's e-mail is:

(sorry, this is not a clickable 'mailto:' hyperlink. If you want to write to Ian, please type his address in your mailer. )

As soon as I had some spare time I set to work at once and made another set of float chambers from these castings.

The float chamber lid castings have a nice projection which can either be used to make them top feed ones, or they just give a handy grip to cut the big threads.

I made a jig with the 45mm* 20 tpi thread to hold the jugs while polishing and making the central hole in the bottom.

So this is the result after the first workshop session.

The twin arm I bored and reamed and put it on a mandrel to face the central bit...

... as well as the bits to which the float chambers will be soldered

Ok, I admit this one was a bit academic: I put the whole lot on the rotary table, as I thought I'd want a cylindrical boss that is exactly at right angles to the aforementioned faces...

... in order to properly chuck the bit for making the holes and threads on which the float chambers go.

The petrol outlet bore was made on the FP1 using the dividing head to nicely align the work...

....as was the second hole in the float chamber.

Now some fiddly stuff: The hollow screw holding the float chamber to the arm.

Mind you, if you can source original ones, they have a 3/8"*28tpi thread, have you got a tap for this?

Please bear with me, I have used a normal 26 tpi cycle thread.

I had to make a special die stock to cut the 1/4" BSP thread where the petrol pipes go, as the second end makes it impossible to use a normal diestock!

I spent a lot of thought whether to make the tickler and clamp bolt holes parallel to the float chamber axis or at right angles to the inclined surface of the lid.

On original carbs I had I found both of these.

In the end I decided a 5° angle looks better.

Still the slit for the clamping bolt needs to be made...

And I almost forgot to drill a quite vital hole!

Another fiddly job: The float needle guide and valve.

Well, that's it , almost!

ok, I still have to make the ticklers!

7/2005: I have now finished the job cosmetically.

To obtain something like the original finish, I give the polished surfaces a light blast with glass beads before having them nickel plated.

And this is how the float chambers look on a bike.

I just put them on my 680 for a picture.

Any kind of feedback to is appreciated
(sorry, this is not a clickable 'mailto:' hyperlink. If you want to write me, please type my address in your mailer. )

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