If you read post #1 he said 1800 RPM was his Idle speed, That is high enough to pull fuel from the boosters and if the vacuum is low it will pull extra fuel from the PV if the PV is under that vacuum.
Actually very unlikely there was enough velocity at 1800 rpm to initiate the boosters in that carb/engine combo - especially out of gear.
And if it did, the vacuum would be relatively high because there is no load and very little throttle is needed.
