Morris Minor Owners Club

Can someone please tell me what the above vacuum tube is intended for. Is it a balance tube for twin carbs? Is it an extra emission added tube to enhance the extraction of bypass emissions from the rocker cover. I mean, its pretty easy to just block it off, bit I would like to know, what the original intention was.

I have one on my carb as you describe. I have always believed it to be for the vacuum pipe to a brake servo which was never fitted. In my case I am quite pleased as I intend to fit a servo later this year.

Do you mean the one to the rear of the carb when installed on a standard minor, and below the dashpot, close to the throttle linkage? If yes, then it's to connect to the crankcase breathing system on later cars. There could well now be many suggestions as to which is the best breather system, and which components you need in terms of rocker cap, oil filler cap and tappet chamber side cover...

If the pipe comes out of the carb body at an angle (similar to the one for sale in the 'e' bay link below) it as mentioned above the connection to the sealed breathing system.

https://www.ebay.co.uk/itm/SU-HS2-Carb- ... SwtC5c2cRD

Easily sealed but your mixture may not be perfect now if the pipe is open or after sealing the pipe.

As regards vacuum take off for a servo - it is no good as the vacuum needs to be created engine side of the throttle butterfly - so a manifold take off is recommended/required.

If it’s the angled brass tube, I’ve seen it fitted with a plastic restrictor. I’m not clear as to why this was.

philthehill wrote: ↑Wed May 22, 2019 10:54 am If the pipe comes out of the carb body at an angle (similar to the one for sale in the 'e' bay link below) it as mentioned above the connection to the sealed breathing system.

https://www.ebay.co.uk/itm/SU-HS2-Carb- ... SwtC5c2cRD

Easily sealed but your mixture may not be perfect now if the pipe is open or after sealing the pipe.

As regards vacuum take off for a servo - it is no good as the vacuum needs to be created engine side of the throttle butterfly - so a manifold take off is recommended/required.

I think the breather down would nave to be in the circuit if the above takeoff was utilised. I vaguely thought it may have been an afterthought anti emission mod. Thanks for your reply

All of the BMC/BL breather set ups are after thoughts - mainly incorporated to continue sales to the USA.
At one stage the BMC/BL 'A' Series cylinder heads incorporated air injection into to the engine to reduce emissions for continued sales in the USA but the equipment reduced the engine power drastically and eventually BMC/BL gave up with the 'A' Series for US sales.

The carb pipe cannot be utilised for brake servo use as there is no vacuum once the throttle/butterfly is closed.

The brass pipe in the side of the carb is technically a take in not a take off as it takes in engine fumes for consumption in the engine.

Can you post a picture of the angled pipe please?

I was wrong about the vacuum pipe. What I have is the manifold spacer with vacuum take-off. A different animal not on the carb body.