Apparently, I need to adjust pump pressure, and have never done that.

The engine is the UAV Bully PR 1.20, a two stroke. This engine is no longer made, but it is a Webra 1.20 with two plug head, back plate regulating pump, and needle valves modified for the pump.

I have two of these. One runs fine out of the box.
I am unable to achieve that with the second. High speed is no problem, but with the midrange proper, it is too lean at idle. As soon as the engine consumes the fuel in the crankcase, it dies. If I richen the low speed to achieve idle, the midrange is too rich, even though I still cannot achieve idle.

The instructions for this engine state: "If the engine stumbles while going from idle to mid-range the pump pressure relief valve (the brass screw and jam nut on back of engine) needs to be screwed out one half turn. After any pump pressure adjustment the carburetor will have to be readjusted" and "If the engine stops or falters during change over to full throttle, the mixture is too rich and the idle needle should be screwed in a little."

I take this to mean that screwing the pressure relief valve "out" reduces fuel pressure; Is this correct? Is there a particular pressure setting, say in pounds per square inch, which would be appropriate? Should I attempt to measure that, or just use the unmount, adjust, remount and try again procedure?