robert:

Regulator - controller - sets fuel pressure.

With the needle setting unchanged, higher pressure forces more fuel flow through the same restriction, making the overall mixture richer.

With the needle setting unchanged, lower pressure forces less fuel flow through the same restriction, making the overall mixture leaner.

And whenever the pressure is changed the needles will have to be tweaked.

This is the hard part about learning to adjust a pumped engine.

But when you get it right you will have excellent throttle response and engine power all the way up and down.

Who needs fuel injection?

And you wont want to go back to muffler pressure.

Bill.