I've never had any luck with the line feed on any weed eater I've ever had, either the bump-feed or the automatic feed kind. The spool always seems to get snagged or hung up and won't feed. When the exposed line wears out, you have to take the darned thing apart and try to finagle with the spool to make it feed.
After going through several years of frustration and all the words in the slang dictionary, I finally came up with a fix that works pretty well. Here's how to do it.
 Open up the canister which contains the spool and take the spool out.
 Set the spool to the side.
 Measure the distance from the outside of the canister to the blade on the edge of the weed eater's hood, as shown below:
 Cut a piece of line from the spool. Make sure it is double the length from the canister to the knife. Tie a knot in the middle of the line. Repeat until you have a good supply of lines with knots tied in the middle. Put them in a container you can carry with you as you use the weed eater.
 Take the cap off of the canister, and stick both ends of the knotted line through the hole which the line feeds through. If there are two holes, do the same to the second hole with another knotted line.
 Replace the cap.
 Weed eat, replacing the line as in Steps  &  as it wears out.
 If the hole is too small to accommodate two thicknesses of line, just stick one end through.
 Replace the cap and weed eat. When the one end wears out, you can uncap and stick the other end through.
COMMENTS: You want to stick two ends of the line through the hole if you can. You get double the cutting power that way.
You want to use the thickest line that will fit through the holes. Thicker line cuts better and lasts longer. I like the orange line. Don't bother with the thin white line. It wears out too fast.
I know I’m not the only person who’s ever experienced this problem with weed eaters. When I go to Lowe’s or Home Depot, in the weed eater section I find all kinds of after-market attachments to put on the end of your weed eater. They wouldn’t be selling those things if the dad gum weed eaters worked properly in the first place.
I like my fix better than the after-market attachments because (1) I’ve never been able to find an after-marked attachment that would fit the weed eater that I bought, and (2) it’s cheaper just to buy more line than it is to fool with the fancy attachments.
Here's another reason I think I came up with a good fix for the problem: Last week I went to Lowe's and found that some enterprising capitalist was selling precut thick plastic lines with knots on one end to stick through the holes of your weed eater canister.