It's adjusts pre-boost fueling. It pushes the AFC diaphragm and foot forward so the rack has to travel further forward before it contacts the AFC foot. If not tuned right you can put out the flame. Read through the AFC tuning thread and you'll be good to go.

I thought you were talking about the screw in the back and not the star wheel. I would be careful when turning the screw inthe back, if you turn it to much you will hit retard notches in the rail and it will not run good until higher rpm.

????? Explain please, I've never heard of adjusting anything in the AFC affecting anything other than the fuel curve.

:pca1:

is there anything to gain by adjusting the smoke screw on the back of the pump? i dont mean the starwheel. my truck doesn't smoke and i'd like to keep it that way, just wondering if there's any power hidden in that little screw?

It increases pre-boost fueling. You can adjust it and see if the truck picks up some and if it makes to much smoke you can back it off.

Does anyone have a pic of the where abouts of the "smoke screw" I cannot seem to find it..my truck runs like crap at low RPM but runs great with a little throttle..maybe this screw is in too far??

Look in the AFC Adjustments thread.

its under a cover on the back of the afc, one screw is a tamper proof screw, i just grabbed it with vise grip. the screw has a jam nut on it

thanks guys..found it.