My 81 300D seems to have air in fuel. (My teenage son may have ran the tank too low and got air in, if that's possible, or may have run out of fuel.) Hard to start. Filled tank and primed over and over and finally started with pushing accelerator down to floor. After driving about 150 miles and tank gauge at about 2/3 full, car started idling poorly, sputtering, especially up hills, and now will not start again, just like before. I have read a lot of posts about finding leaks in the fuel system. But my main question is about the fuel primer hand pump. Mine does not seem to act right. My owner's manual says to rotate the primer handle counterclockwise to activate it, but mine will turn either direction indefinitely and it doesn't seem to make any difference. (The top on my primer pump that I grab to pump it is black plastic.) I'm thinking I'm not doing something right or the primer pump is not working because it never gets any more difficult to push down no matter how long I do it. What does it mean to "activate" the primer pump? Any experience with this or any advice? Thanks.