The system works entirely on vacuum that's sourced in the throttle bore of the mixer. If there's low vacuum in this circuit it may be low enough to not turn the regulator "on"- so to speak- especially while cranking while engine vacuum is at it's lowest.

I would check the hose between the mixer & the regulator- even a pinhole in this line will make a big difference.

I wouldn't run the lift w/out the PCV system working- the engine is designed to "breathe" & just venting the engine will cause excessive sludge buildup, etc.

In answer to your question- is it an on- off system?- The fuel system is a constant flow type that is controlled by the vacuum pull of the throttle bore of the mixer. This vacuum works against diaphragms which are spring loaded- there are different regulators which flow different flow rates at the same vacuum.