What does this do?

[Tea]

What is the purpose of this part of the vacuum advance?

[Chipper]

I gather it is a 'flame trap' to prevent possible damage to the vacuum advance diaphragm in the event of a backfire from the carb.

Later 1098cc models didn't have it fitted.

[irmscher]

They didn't work

[GavinL]

You can omit them and fit plastic vacuum pipe work as fitted to MG Midgets and others - I've just bought the pipe and fittings from Moss for £4. Only thing is the fittings are push fit so might need slight modification to work with the screw threads.

[Tea]

Ah I see. The rubber tube connection on our plastic one had corroded and split, so fitted one of these ones. It didn't work and the engine ran as though we hadn't fitted a vacuum advance so got a new piece of tubing for the old plastic pipe which now works a charm. Bit of a waste of ~£25.00