the timing wont change unless you rev the motor when you do that the pressure changes in the manifold which pulls the plunger advancing it when the idle comes back down it pushes the plunger which retards it, but i believe you are right, to set the timing you unplug the two hoses from the advance but cap them off temporarily, you are going to have 2 forms of advance the first is mechanical weights in the distributor and the second is vacuum at least that's how it was explained to me. when i had a problem with mine my shop teacher told me that the vacuum advance was for cruising and if you hit the gas the weights are already out so they cant advance the timing that's were the vacuum comes in
