Valve stem questions

[sick 96 250]

Ok for some reason my valve stem is letting air out of my tube on the front. It was doing to the last tube I had in there and i thought i had a piched tube from riding but once i took the tire off i noticed it was just the valve stem. I ended up putting in a brand new HD tube anyhow and kept it as a spare. I went riding the other weekend and hit a few nice size rocks that were mounted in the ground with my front tire and thought i may have pinched that one as well because I was running a slightly lower air pressure for the conditions I was riding. I added some air after that from my pump and it seemed fine all day, got home and when i unloaded my bike it was flat, so I pulled the tire off again to change out the tube and same thing happened, tube was fine but the valve stem was leaking slowly. All I can figure out is possibly my foot pump i use is either getting debris in there or something else is going on. Any way to figure this out? Isnt there something that can pull the little release piece out in the stem and rplace it or something. I just cant figure out why two perfectly fine tubes could do this and have the exact same problems.

 

[FruDaddy]

Pull out the core and take a look, if it's dirty clean or replace it, you can get the replacements at the auto parts store. When you reinstall the core, make sure it's tight.

 

[sick 96 250]

yup, i got fed up and went to the autoparts store and picked up a little kit for like $5 that had 4 cores, the tool that takes em out, psi reader and some chromies and regular caps. As soon as i got back and i went to pull the core piece it was really loose for some reason, i took it out cleaned it up a lil then put it back in and made sure it was tight and filled the tire back up, i dont hear any air sneaking out but i will give it the overnight test at least and see where i stand. I do have one other question though, my first original tube that i had out was doing the same thing, when i pulled the core piece out it had a spring attached to the bottom of it, what is that for?