vacuum gauge to solve idle issue

Ok, First off was the vacuum advance hooked up during the surging?And where to? And secondly I think the power pistons were popping up.And third;as mentioned the choke needs to be off, and the engine fully warmed up, for any meaningful diagnoses.Unless this behavior only manifests during the warm-up period while the choke-blade is engaged.
And fourthly; carb size.You are idling on the primaries so it is almost, I say"almost" irrelevant as to 500 or 600cfm. If you like, I'll put an 850TQ on and it will not be too big at idle .These style of carbs can be adjusted to work well outside the formula, especially as compression and cams go up..

Ok so now, here's my thinking;
For an engine that is just warming up;if the vacuum advance was hooked up to full-time manifold vacuum: With the choke having set the fast idle cam;engine vacuum brings on the vacuum-advance. But the too-far OPEN choke blade causes the cold engine to run out of fuel,so it slows down, and manifold vacuum drops.This triggers the Metering rods to rise, which dumps fuel in,while simultaneously dropping out the vacuum advance. The extra fuel causes the rpm to rise and the vacuum to build, and that pulls in the Vacuum advance. And so, on it goes.
With the Vcan hooked to the Spark-port,at least the timing would be stable, unless you have a really fast curve in the dizzy.But the rest of the scenario still holds.
But this scenario only works during the warm up period while the choke blade is set, and the engine is relatively cold. As soon as the engine warms up and more importantly, as the choke blade retracts, this behavior would stop.
So to help in diagnoses, try this;
-Make sure the vacuum advance is NOT working at fast idle, by unhooking the can and plugging the line.
-Also make sure the PCV has a stable operation.
-To prove it is a power piston problem, you just need to de-activate them; at idle they should not be working, hot, cold or anywhere in between. You can do that by popping the springs out from under them, and dropping the assemblies back into the jets. This circuit is not used for idling.
-Put a clamp on the vacuum line to the power booster, if you have one.
-If the problem persists, fire your mechanic(me,in this post).....He don't know sh.....lol