The discharge hole is pretty big on 1969-70 Pontiac units, but tiny on other models.
They also put a tiny restriction in the supply tube on some as well.
The idle for primary POE was to run a very lean mixture for light part throttle (normal) driving, then pull in additional fuel with heavier throttle movements/increased engine load. They did this without increasing fuel delivery from the accl pump so and it will continue to add fuel not just a single shot with a quick throttle movement.
I've played around with it some and have simply found it doesn't really offer anything over nailing down the correct primary side tune right to start with.
The problem with tuning is that folks associate "lean" with improved fuel economy. Attempts to go leaner than the engine will tolerate result in the operator having to increase throttle angle to pull in more fuel to make the engine happy, therefore increased fuel consumption.
The key to tuning is to find out exactly what the engine wants over the entire load/speed range. Distributor tuning is equally important, and the vacuum advance a BIG player on engine efficiency at light load.
To this day I continue to talk to folks, even shop owners who are "old school" and stuck in the 1960's when it comes to distributors. They eliminate vacuum advance after installing distributor "kits" in bring total timing in sooner thinking it isn't needed.
Nothing could be further from the truth. The vacuum advance is a load sensing device, and only in at light throttle and when vacuum is high. It is NOT in at heavy/full throttle, so no negatives anyplace in using it even with your fast advance curve.
Increasing timing at light part throttle allows for leaner mixtures to be effective burned, so use it as part of your carburetor tuning........Cliff
