TR2/3/3A TR3 SU carb question

[Lukens]

The carbs on my TR3 were replaced at some time. What is the purpose of the "vent" nipple coming directly out of the carb body? The previous owner ran a hose from one to the other. Is this to balance air flow? Pollution? Necessary?

Thanks,
Russ

Edit: Oops, forgot the pic:

 

[Geo Hahn]

Certainly not necessary nor even useful in my opinion.

Brings to mind this recent thread: https://www.britishcarforum.com/bcf...ve-strange-vacuum-fitting&p=879026#post879026

Though at least the placement on yours seems like it might get at real vacuum.

The TR3 manifold has a pretty big balance tube connecting 1&2 and 3&4 so that puny hose isn't going to have much effect.

I suppose one possibility is that someone thought they were learning something by attaching a vac gauge at that spot and the tube was just a way of closing off both fittings. Yeah, far-fetched.

 

[Geo Hahn]

Upon closer examination -- those are not TR3 carbs. So, anything's possible.

 

[donbmw]

The only vacuum port I have on my TR3 carbs is the on the bottom of the front carb and this goes to the vacuum advance on the disturbtor.

 

[titanic]

The carbs are hS6s (from the emission control era) and the nipple connections are for crankcase ventilation. I use the same carbs on my 6 and the hoses run to a nipple on the valve cover. On a 3, just plug the nipples and use the road draft tube. Berry

 

[Lukens]

You confirmed my suspicions. These carbs have the float bowl connected directly to the body. Mine were not tight and were weeping fuel.
Do you have a site, pic, article, ?, that addresses these late model SU's?

Thanks for all the responses.

 

[titanic]

The same carbs, SU HS6s (minus the crankcase vent nipples) were used on TR4a, so all of specs should be the same. Check out the Moss catalog for detailed pics. Make sure the float bowls are level (north-to south) as the carbs are used on many applications are adapters are used according to the angle of the manifold. The only way the float bowl can leak is where the jet attaches at the bottom or at the lid gasket. There is no opening where the float attaches to the carb body. Berry

 

[Darrell_Walker]

The only way the float bowl can leak is where the jet attaches at the bottom or at the lid gasket. There is no opening where the float attaches to the carb body.

The jet tube connection to the float chamber is a very common place to leak. Moss has a video on how to make sure that connection is good:

https://www.youtube.com/watch?v=ZPzu2zzyGCQ&list=PL272A5378FCE985B8&index=44

 

[titanic]

Darrell-Very true. I have found that a -008 o ring makes a good substitute for the seal and is available locally. I meant that the loose float bowl attachment bolt would not cause a leak. See you at the Montgomery Park swap meet Sun.? Berry

 

[Lukens]

The only way the float bowl can leak is where the jet attaches at the bottom or at the lid gasket. There is no opening where the float attaches to the carb body. Berry

You're so right. I see now that the weeping was coming from the bottom of the bowl. Jumped to a conclusion when I saw traces of gas that driped down on my heat shield.

 

[Darrell_Walker]

See you at the Montgomery Park swap meet Sun.? Berry

That time of year already? Probably not, but hope you find some good stuff!