Would someone please tell me how this darn thing works......

I have one without instructions......Was using it on OS 108 which was working great......But now find that nose up....the engine dies
and no amount of needle twisting has any effect.....

Pump has in/out at the bottom with a hex screw......Top has a nipple which I assumed was connected to muffler pressure to operate pump.......Spent 2 hours at the feild today messing with this engine............After reading old threads in this forum ,,I am to understand that the hex head on bottom actually controls maybe the flow ????

Carb on this engine is a 7D......

Thanks