Vacuum Advance

[6Bcygnet]

I have just fitted a new vacuum advance to my P6B.
The timing has been set according to the manual ie 6 degrees btdc.
I am curious because on idle, there is no detectable suction on the tube from the carb. I would have expected a vast reduction in manifold pressure.
On opening the throttle just a small amount, there is considerable suction apparent. As I would expect.
With the suction tube connected to the Vacuum advance the timing light shows appropriate advance.
Bob weights work and the car runs well.
Does the carb slide block off the vacuum suction tube when closed?
As a point of interest the car runs much more smoothly and the acceleration is more lively.
I think!
The placebo effect may be operating on me, but i don't think inanimate objects are susceptible to it - or are they?

 

[JVY]

inanimate objects are susceptible to it - or are they?

It just depends how you look at them .
I don't know if the vaccum advanced is blocked off by the carb pistons at idle. However, I certainly wouldn't expect any suction at idle.

 

[1396midget]

depends which side of the butterfly the vacuum take off is. Engine side, there will be vacuum at idle, filter side there won't be and it'll behave exactly as you describe.

 

[6Bcygnet]

Thankyou,
I was assuming, incorrectly, that the take off was on the manifold side of the butterfly.
Hence the confusion.
It certainly makes a difference with the vacuum advance working correctly.