line flies out of troy-bilt trimmer WAY TOO FAST!

Is there a fix or work-around for this problem? Our weedwhacker, a gas powered Troy-Bilt (like the Ryobi) used to let the line out properly (when we bumped it on the ground) but now, it lets itself out - it's always at the max length and chops itself off - I never bump it and it runs out of line very fast. we had the bump knob off and cleaned the assembly, did not see any obvious problem except the foam seal is a little bit torn.
Help? Jane

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
Add image file
Upload is a website for homeowners and building and maintenance pros. It is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.