For the Air/Fuel ratio control valve; Less fuel (less black smoke, until boost increases) = loosen jam nut, then "loosen" or go counter-clockwise (looking from rear of engine) with the inner screw (use small screwdriver, but hold that aluminum cone with pliers or small vise-grips) Note: you should see more threads, behind jam nut, when done.

Now, if diaphragm is blown, BUT you still readjust(lean out) the air/fuel ratio control valve = you will have "Low power", constantly = you need to make sure the diaphragm is OK (holds pressure), first.

 (you can adjust those, soooo lean, that they will even kill the engine, on deaccelaration)

Now, there is always the possibility that "whoever" installed the air/fuel ratio control didn't get the internal plunger "latched" onto the internal fork assembly = that would make the whole air/fuel ratio control totally worthless = won't restrict any fuel, because linkage isn't attached, internally.

(3406B rear governor housing_in paint program.jpg)

3406B rear governor housing_in paint program.jpg (113KB - 1376 downloads)