Possibly (another) stupid question

[tvr4ever]

While looking at the ignition I wondered. The vacume advance tube is connected to a small membrane (?) wich in turn moves something inside the ignition. (eeerrr so i think). How can you test this if it works. I tried sucking the little tube and looking at the ignition but i can't see anything move. Should there be anything moving ??? According to the bible many people do away with the vacume advance, what are the (dis)advantages.

Fred

[KeithS]

Oddly enough I was doing this with my vacuum advance tube only yesterday, while we were rooting out the cause of a bit of rough running. No matter how hard I tired, I couldnt see anything move, but I think that the black cap that is visible when the dizzy cap is removed might be static and the moving part is under that. That or I don't have enough lung power to make it move in the first place!

I would have thought that the vacuum advance is a necessary piece of kit or it wouldn't be fitted.

[GreenV8S]

It increases the advance at part throttle, improving economy and all that stuff. Makes no difference at full throttle, hence people who are only interested in absolute power often can't be bothered with them.

[david beer]

If you give it a "suck" while the engine is running, the engine speed will increase. Another test is to give it a suck and pop your tongue on it and see if the vacuum dissapears. I have replaced four in six years, but as Peter said it does nt affect flat out performance.

[nobbie]

The diaphragm had gone in mine and was responsible for rough running on part throttle (30-35mph in 4th/5th). Had it replaced (under warranty) and it was like driving a different car