In General:
Vacume Advance:
There are three types of vacume advance setups.
1. Being straight manifold vacume { This type usualy incoprorates a V.R.V. {Vacume restrictor valve} {This valve or something like it can be incoporated into the vacume advance moduel itself Eg. a vacume bleed off port} to prevent the advance during idle conditions} Among many other various vacume operated valves on the emission system.
2. Being ported vacume, either connected directly to the carburator above the throttle plate or connected to a thermal valvebody attached to the intake manifold which in turn is connected via vacume hose driectly to manifold vacume, incoprorating many emission related vacume oprerated valves and gizmos. This thermal valvebody is only active at O.P. temp.
3. Bieng a dual advance/retard system. {two vacume lines from the vacume advance/retard pod on the distributor.}This system is dependant on the emissions system being left intact and working properly.
There should be NO active vacume advance while the engine is in an ideling condition. If there is, something is amiss, the V.R.V {If your system requires one} could be malfunctioning or removed ETC.
The primary function of the vacume advance system is
to increase engine timing on acceleration for improved power and to increase timing advance in a cruise condition to improve gas mileage, eg. economy.
Vacume advance malfunctions will have a great effect on engine timing at above idle conditions but should have little or no effect at idle conditions.
The centrifical advance will have an effect at ANY engine speed! It is best to ensure that the centrifical weights are intact and operating freely and the springs are correct for the advance curve you desire or your engine requires.
ANY advance in timing WILL increase engine speed at idle. Static timing is Just to get you in the ballpark.
As stated above, It all works in conjunction, idle speed, and timing. Once the initial timing is set { Vac Adv. dissconnected} reconnect the vac advance and recheck the full advance condition {Being a specified advance in degrees {example only EG. 34*} at a specific engine R.P.M. {example only eg. 2,800} set by the manufacturer}{usualy a cruise condition R.P.M.} to see if it meets the O.E.M. specs.
NOTE: Too much advanced timing is NOT a good thing for your engine!
<span style="font-weight: bold">This is ALL just GENERALY speaking</span>, Your car may have "other" gizmos, gadgets or equipment attached to the vacume circut that can {and usualy does} have a profound effect on vacume preformance items such as the vacume advance module.
I hope this info at least gives some insight to anyone that is going to attempt removing, rerouting, Vacume lines or related devices. The Vacume advance can be dependent on some or many of these devices especialy on newer vehicles. Or {Like me} trying to figure out what someone else that has no idea what they were doing and removed ALL traces of vacume hoses and related devices from an engine. Then wonder why it wouldn`t run very good!
P.S. YES ......... the Idiot left ALL of the vacume ports uncapped too! GO FIGURE!