Design For Machining Vacuum Take Off Point For Old Style Carbs

The restriction in the fitting is to reduce the size and speed of the pulsation in the tubes. If you look at some YouTube videos on carb sync, you will see that when using colored fluid in the tubes the fluid bounces around quite a bit. Thus the restriction.
Pierre
 
Pierre

The rubber tubes have small screws on my unit which dampen down the flutter. Just trying to sort out the actual size for the inside of the spigots. At present looking at a 1mm hole.


Mal
 
You may be right. When I made mine, I used a 1/16th drill and I believe it was still too big. I may fill the hole with solder and re size smaller for the next time.
 
well looks like off to the machine shop for some number drills.

Dropped into my metal supplier today but he is closed for end of year stocktake - well that will have to wait till next week.

Mal
 
Cascao

You are 100% right - I found this out once I pulled out my metric taps and Dies. I originally did a poor job measuring the a 5mm thread with my thread pitch tool.

Thank you for pointing this out.


Mal
 
well looks like off to the machine shop for some number drills.

Dropped into my metal supplier today but he is closed for end of year stocktake - well that will have to wait till next week.

Mal

You might want to check out a welder's supply store for torch tip cleaning drills. Quite tiny they are.
 
carbalancer.jpeg I used one of these to great effect on twin and triple SU's and also on .Honda4's very cheap, and no machining necessary. Also seen a 3/8" thick aluminium gasket with a vacuum take off point tapped into it fitted between carb and engine. Good luck with it!
 
27380587493_a3f9a579db_c.jpg

I had an old carby body, so knocked up a screw in spigot - just to test the concept machining wise. In this case I used a 1mm drill - maybe OK - maybe still too big. Thank you to all who made suggestions - no hard decision has been made at this stage. The bike is up and running, however tuning was just by ear and feel - it's OK but I am sure it could be a bit better.


Mal
 
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