Originally Posted by fasteddy_1947
you don't want vacuum at idle. Need to take the timeing advance vacuum from connection above the accelerator valves, so that when they open, they advance the spark. You'll find it hard to set your initial timing if the vacuum advance comes from the manifold, which it will if you connect it to anyplace below the throttle plates. easy nuff to find a connection. open all the vacuum hoses, one at a time, with engine idling, until find one that doesn't change the RPMs when it is open. it will be above the throttle plate, and will create a vacuum when throttle is opened up.
The debate on using ported or manifold vacuum has raged for years
The timing advance curve can almost always be tuned to use manifold vacuum for the vacuum advance- and there are good reasons to do so. In many cases using manifold vacuum will give better throttle response and will allow the curb idle to be set low enough that the transfer circuit isn't being used for supplying idle air/fuel mixture.
BUT in some cases using ported vacuum IS the better choice, like if the cam is big (low vacuum), requiring a large amount of initial timing. Then, using ported would be the preferred way.
Some info here