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Curious Carb "Accessory" 55 BN 1

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Gray_Cat

Gray_Cat

Jedi Warrior
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I've rebuilt and tuned the carbs on my 55 BN 1 (many thanks Dave!) and have a questions about a couple of "accessory" items on them. At the bottom of both carbs there is a very slender tube (copper) that is plugged at the end with a very small hole just before the plugged end. Each tube is atached by a fitting to the bottom of each carb and are about 5 inches long. I've never seen anything like this and cannot find reference to them in my SU manual or shop manual. Anyone know what they are called and their function?
Many thanks - Roy
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If I am understanding you correctly I believe these are "overflow/drain" tubes.

I think there is a reference to them in

Austin-Healey 100/100-6/3000 Restoration Guide (Authentic Restoration Guides)

Bruce
 
I believe that you are referring to the "manifold drain pipes"
You can see them as item 36 here:
https://www.mossmotors.com/Shop/ViewProducts.aspx?PlateIndexID=28851&SortOrder=35#top

They are originally long, small bore pipes attached to the bottom of the intake manifolds. Note that they extend to approximately the oil sump flange. The purpose of them was to "drain" excess fuel caused by flooded carburetors. Their very small bore & long length prevented them from inducing a major manifold air leak.

I personally consider them to be an unneeded extra since the carbs shouldn't be flooding in the first place & it is questionable how much fuel they could drain out anyway. I just soldered the fittings closed & left the pipes off. Moss lists them as not available. With millions of cars running around with no manifold drains, I don't personally think that it was a particularly good idea. I have never had an SU carb in good condition flood.

If you feel that the drain tubes are an advantage, or wish to be totally concours correct, you will need to find some very small bore tubing that can be full length. Note the small holding clips down near the oil pan flange. The long length & small bore reduces the effect of the air leak into the manifolds.

It appears that on your car, someone has used shorter pipes with a small drain hole drilled near the plugged end. While it will probably work, the problem is that the short pipes will drip fuel on the hot exhaust system. Not so good! Later engines used a short metal pipe with a plastic hose extension. The plastic tends to melt & is hard to route out of harms way. The tri carb engines did not have the drains. Take your choice.
D
 
I found them at British Car Specialist along ith the metal holder at the oil sump. I am not sure of their need but there seems to be a few drips after the engine is turned off which seem to evaporate. I couldn't tell you if it drips while running. But mine connect to the bottom intake manifold. I didn't get that from reading the post. But I have a BJ8.
 
Many thanks guys! I misspoke saying carb when the tubes attach to the manifold. I managed to move them enough that I believe it is safe to leave them on for now. I may remove or plug them later, I just had never seen anything like them before.
Roy
 
I would go with long ones or plug them. Short ones drip in dangerous spots. If you plug them, all you have to do is remove the "nut assembly" at the manifold and drop metal disc(nail head)into it and screw it back up. Thats how mine came from the PO.
 
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