Twin H4s

[johnv]

Am I right in assuming nobody runs a vacuum advance with these?
Thanks

[Daz1968]

I have run a vacuum advance on mine, used an mga vacuum advance pipe, not sure if I needed to or not but as my distributor had it so I used it.

A18A14D7-E7EB-4A2B-AC3F-2B9E6DE62AEC by darren carr, on Flickr

[johnv]

How do you connect it to the carb Darren?

['S'-type]

On the underside of the choke tube to the right as you look at them from the front, there will be either a blank boss in the casting, a drilled and plugged boss or a brass fitting to plumb in a vacuum pipe. This could be in the form of a nipple.
So if you have a pair, you'll probably find one (left side carb) blank. The other should be drilled and capped if they were from an S. You would just have to screw in a union in place of the cap bolt. I don' t know what the thread is.
Sorry to jump in , hope this helps. Pics of the three scenarios:

[Daz1968]

As my carbs were off an mga there was just a threaded hole in the carb and the mga vacuum pipe came with correct union. It’s a little tight for installation but does just clear everything

[johnv]

Thanks for that. Mine aren’t tapped so I don’t think I’ll use vacuum advance. Not sure what the downside to that is though, but plenty don’t have it I guess!