[jlsanborn]

The PCV (positive crankcase ventilation) valve is normally open at zero manifold vacuum (engine off). At idle you have high manifold vacuum that nearly closes the valve. Combustion chamber blow-by is low at idle, so you don't need that much flow anyways. At idle you will have minimal "un-metered" PCV air entering the intake. Under load, vacuum drops and allows the valve to open. Blow-by increases under load but now there's an open path to the intake. At higher revs the amount of "un-metered" PCV flow is minimal in comparison to the "metered" air.

Without a PCV you basically have a big vacuum leak. At idle or low RPM that vacuum leak is substantial in comparison to the "metered" air and will cause the lean bog or hesitation when you open the throttle. Once the revs come up, that vacuum leak becomes small in comparison to metered flow.

The filler tube with the hose barb on the side and the non-vented cap are available on E-Bay. I'd check them out. I bet a PCV cures your lag and you'll rest easy knowing there's a clean breeze keeping that motor cleared out!

My sketch is not real accurate. I'll re-draw that tomorrow for clarity.