Mercedes Benz repair: 1983 300sd starts, runs and stalls, stale gas, dieseling

Question
I bought a 83 300sd two years ago for $500, i recently had problems with power climbing hills and then the car would act as though it was running out of gas when im sure there is fuel in the tank.  I use the manual pump near the engine block to feed fuel into the engine, it runs for a few minutes but i can see air in the fuel line that eventually goes away after the car has sat for 10 minutes.  i dont see/hear any leaks in the fuel lines and no clogs that i can find.  i also have to pop the hood and hit the shut-off shiwch on the engine every time i drive to make the engine stop dieseling, im not sure if there is a connection between the two but any help would be great

Answer
http://www.benzworld.org/forums/w126-s-se-sec-sel-sd/1376495-300sd-runs-rough.ht...
go to benzworld.org fill out a profile it seems it may be your prefilter or fuel filters  may be clogged with old stale gas .worked for this guy as far as the dieseling or run on im not sure what switch you are talking about I would like to help you more but I can assure you he people at benzworld.org can help you better with your diesel