Originally Posted by Baja

Next for the AFC.....several adjustments there, but not everyone understands them completely. At this point we know that the AFC is there to limit fuel supply during low, or no boost conditions. That's itsa only function, cut and dried, don't let anyone tell you differently. With a stock spring, after about 6 psi, no more AFC influence on the pump...that simple. If you have low tension springs in it, cut that down to about 2 psi. We know that the AFC lever protrudes down into the pump cavity right next to the fuel plate, and at no or low boost, it catches the gov arm and limits fuel that way. So what are we doing by moving the housing forward? We are simply moving THE ENTIRE ASSEMBLY farther to the front of the engine which allows the gov arm to travel farther which allows more fuel....that simple. So what about the star wheel? That wheel acts on a spring that pre-loads the pressure diaphram which is boost controlled. If we turn the starwheel towards the engine, it moves forward, releasing spring pre-load on the diaphram. As this pre-load goes away, it takes less boost to act on the diaphram and move the AFC lever out of the gov arm travel path. We think of these as the fine and coarse adjustments for the AFC, which is not totally true. The coarse adjustment is indeed moving the housing itself. But the fine adjustment is not the starwheel.....it's the so called smoke screw. You don't see this becasue it is on the back of the AFC housing under a sealed cover with a break off crew. This screw actually bottoms out on the diaphram center...from the boost side of the diaphram. And what happens when we add boost? The diaphram moves the AFC lever out of the way right? So by screwing this stud in, we give the lever a head start getting out of the way...much like moving the housing. That is why it is truly the fine adjustment. So we can set the housing in one position, then fine tune that position with the smoke screw. These adjustments alone will influence off idle smoke....not the star wheel. The star wheel will influence how long it takes to come off pre-boost fuel and into full fuel. So lets tune a pump...