I just bought a 1980 shortbed pickup with the 20R engine in it. The previous owner had bypassed the mechanical fuel pump and replaced it with an electric fuel pump. There is a tee going to the carb with one end going back to the fuel tank for some reason??? Anyway the truck runs great most of the time except when going on semi steep inclines{highways not off road)such as over passes or in the mountains. When the incline reaches a steeper degree the truck feels like it is running out of gas and stutters a bit. Seems a little better when I let off the gas a bit but not always. Just curious if you guys have any suggestions or advice for me?? Thanks in advance. John

Also what would happen if the tee was not there and the fuel pump psi was going all to the carb??

OK here is an update. I didn't get any replies before, but circumstances have changed. Took it to a mechanic and they said the carb was shot so I bought a new carb and had it installed. Now it is doing something different. It starts only if I press all the way down on the gas and then runs rough. After driving a while and come to a stop it wants to stall. It seems to run fine while in gear and driving down the highway but doesn't want to idle. The mechanical fuel pump is bypassed and has a electric fuel pump installed. What are the return lines for? Thanks for your help in advance John