Fuel related issue on rear engine

[YankeeClipper]

The io360CB in the rear--long in years, short on hours (10ish vs. 100ish)-- doesn't like to start. My IA decided to give it a go with the low aux pump on, but to no avail. We moved on to the high, and lo and behold she started, and quickly at that. But not for long. Short form: I had to manually meter the flow through judicious application of the high pump--on ... off ... on ... off--in order to maintain some semblance of a smooth idle.

That IA surmised either rear engine fuel pump, or the flow divider. The IA that's currently working on it said that the quasi-success of the aux pumps should rule the flow divider out, and so it must be the engine pump.

Having said all of this, I think my question is likely more academic than practical. It is:

Do these engines not have fuel pressure regulators like their automobile counter parts? Hard to imagine they wouldn't, but if they do, why would I need to back off the aux pump to keep it running?

My (sorely missed) 1971 Benz 280SE with mechanical fuel injection had such a thing. Even if the pump pressure for some reason exceeded normal, it wouldn't become an issue until something actually leaked or ruptured. But until that point, the injectors would received their holy 56-60 lbs/inch as the engineering gods intended. Not more, not less.

Any thoughts appreciated.

-Gray-