Question of advance.

[steveko]

As far as the vaccum advance on the distributor is concerned I read that the stator should advance and hold at 20in Hg of vac when vaccum is applied to the outside fitting. Is this too say that any less of vac it shouldn't move? Anyone know where their advance stays at vaccum wise and holds at because mine comes in and holds at like 5inHg way lower than suggested in the manual.

[shepherd79]

the vacuum advance will move around 5 inhg, the reason they say it should hold 20 is because that is what your engine should produce when idling.

[2oodoor]

that is not really a specification I was ever concerned with, unless it didnt hold well enough, yours sounds to hold excellant.
The fitting is attached to an almost air tight cavity with a diaphragm which has an accuator linked to it. They are called vacuum motors in most other applications, except in distributors they are called vacuum advance ><
There are some available for USDM that have an adjustable stop inside the fitting to adjust how much vacuum it takes to move it. I guess that in some tuning settings for advance curve+ vacuum+throttle opening+engine load sychronization.. so I guess there is some concern for how little vacuum it takes to move the accuator.
There are two different advancing vac diaphragms on most of these cars, and yes one does respond at lower vacuum than the other..two stages sort of.

I

[steveko]

I actually replaced the unit 2years ago due too it not holding.If I remember correctly it's a Hitachi distributor. And your correct I thought the advance was comming in too soon due to a hesitation at 2000 rpms. which may not make sense anyway.