SU H6 carb question

[Michael Oritt]

Some time ago I removed the Cold Air Box on my car's H6 carbs which were part of the Le Mans kit installed by the original owner in 1956 and replaced it with velocity stacks. I have not yet removed the short "Vent and Drain Pipe" which went from the top of each float chamber through a hole and grommet and into the CAB. If the drain pipes serve any purpose it stands to reason that I should now replace the short ones designed to work with a CAB with non-M drain pipes which lead down and, I assume clear of the exhaust manifold and pipes.

Moss pictures what I believe is the correct non-M part on p. 24--pn# 97/451-250 but describes it as "Vent and drain pipe to cold air box, 100 M". I believe the illustration is correct for the H4 original setup, not the one for an H6 Le Mans CAB setup. I think this may be important as I seem to recall that the the two vents utiize different fiber washers, the non-M setup using a conventional washer and the M setup using a "scalloped" or vented washer.

Can anyone please enlighten me on the correct parts I should be using?

 

[CraigC]

I don't have part numbers, sorry.

The banjo of the vent tube has a small opening on one side and a large opening on the other. The large opening faces down towards the float bowl. This side uses the washer with the 3 cut outs on the inside edge. Top washer is solid.

The vent tube should be short, not even long enough to reach the bottom of the float bowl, just like the stock H4 vent tube.
If you go to Joe Curto's website he has plenty of images to peruse. TR3 or TR4 pics should show you what you need.

Edit: went to Curto's site and found the TR3 H6 carbs have an oddly curved vent tube. I thought the one on my spare carb was damaged , but matches the pic. The Elva Courier MGA with H4 carbs show what I remember to be on the AH 100 H4

 

[Michael Oritt]

Craig--

Perhaps I am confused but thought that "stock" H 4 or H6 carbs--stock meaning used without a Cold Air Box-had long copper vent tubes much like those for the intake manifolds. (I don't know where I got that image in my mind as the car came to me with the CAB, etc. already mounted, etc.)

I will check out Curto's site but if things are as you say I wonder if there is any reason to change out the present ones which do point slightly up from level to enter ther CAB holes. In any case thanks much.

 

[CraigC]

If you have air filters, run them into those. If all you have are the velocity stacks without any filter housings, then I would just set them like the Courier pics on Curto's site.
Years ago when I pulled the CAB off of my M due to cracks, I fitted short, flared transitions inside of Lynx-style filter assemblies. I ran the stock vent tubes right into the filter housings.
Remember, the purpose of the tubes is to allow atmospheric pressure into the float bowls. Any thoughts of them being overflow drain tubes is very much a secondary purpose.

 

[Michael Oritt]

"The Elva Courier MGA with H4 carbs show what I remember to be on the AH 100 H4"


Craig--

I'm not finding that--any chance you can send me a link to it?

 

[CraigC]

Here you go --->http://joecurto.com/elva-courier-su-h4-carb

I may also have some old H4 from a 100. I'll check later if they still have float bowls and vent tubes.