It's a balancing act. The higher the compression and the shorter the cam duration-the slower the advance curve acceleration has to be and the lower the initial starting point has to be. The total mechanical advance does not normally change a lot-just the starting point and how fast it increases to the total.
That is the simple part
When we add vacuum advance to a non stock mechanical advance curve, things can get difficult quickly. Vacuum advance, while complicated at times in non stock situations, should actually be a good thing. It is further complicated by automatic or manual transmission selection with manual transmission being the easiest because it imposes the least load on the engine and therefore, the least effect on the vacuum of the engine.
In the earlier days, cars used manifold vacuum to operate the vacuum advance. Low load, high vacuum-more advance, and vice versa. Then NOX emissions control came along and to lower NOX, you need less advance so factories started producing cars with low initial timing and ported vacuum advance to keep the NOX down at idle and low speed. This was not good for low speed performance at all but it was good for NOX reduction.
I said vacuum advance was good prior. It's good because it should increase gas mileage while cruising and produce a much cleaner combustion burn at teh same time. What makes it complicated are the variables we introduce.
We crank up the initial advance and increase the rate of acceleration the advance curve and we can end up with too much advance at cruise rpms...instead of the desired 50-55 degs of advance, we may end up with 65 degs or more and that brings in light throttle detonation because we lit the fire while the piston was too far down in the hole and combustion pressures are peaking before TDC instead of 15 degs or whatever is optimum for the cylinder head design AFTER TDC. Nice rattle that is not doing the rings, bearings, etc. any good over the long term. So the knee jerk reaction is by far the simplest...disconnect it. Running manifold vacuum instead of ported vacuum may make it worse at even lower speeds.
The easy way to fix it is not use vacuum advance. The best way to fix it is much harder-we have to limit the total amount of vacuum advance allowed as well as how fast it comes on.
With a stick shift, not as much load is placed on the engine at idle when the clutch is depressed and manifold vacuum does not usually suddenly go away with this load so it can really help idle quality on modified engines. Automatics usually drop the vacuum quite a bit when the car is dropped into gear and the idle quality that was much better in Park can suddenly put into gear. In this case, manifold vacuum can make a difficult situation worse. This is aggravated by modifying the engine with longer cam durations, etc. Top that off with a torque converter that is too tight for the cam to begin with and it can make you want to cry.
It separates the tuners from the guys that read the magazine articles without understanding the total picture.
Now, having said all the above, I wonder what is up with your carburetor. Having to open the throttle blades all the way makes me think the car is not running on the idle circuits any more but is either on the transition circuit or even higher. Something seems to be up with that. Typically, the more modified the engine, the richer it will need to be at idle. If the idle improves when you choke the engine a bit, then it may simple be too lean for the engine at idle and opening the blades allows it to pull more fuel from elsewhere.
