How do i get the cover off the toro 11" electric trimmer so that i can replace the string

There is no primer bulb on an electric string trimmer. Is this a trick question?????

All I can do is refer you to the manufacturer's instructions. See page 5 after downloading your user manual. If you can not turn the cap off, then the cap is possibly cross threaded onto the shaft end and/or the threaded end if the driveshaft is stripped. See if the user instructions are of help to you.

http://www.toro.com/en-us/Homeowner/Yard-Tools/Trimmers/Pages/Model.aspx?pid=51347-11-Inch-Electric-Trimmer

Here is a parts and diagram breakdown on your machine. It also includes a list of any and all parts that you can purchase to repair it.

http://www.ereplacementparts.com/toro-51430-500000159999991985-trimmer-parts-c-121776_123781_124021.html

All I know to help you would be parts replacement as plastic parts are wear items and have to be replaced. Here is a parts w/diagrams breakdown of the 1981 model year Toro 1100 trimmer. I hope this can be of help. You can order parts here to replace your "worn out" string head and spool.

http://www.partstree.com/parts/?lc=toro_consumer&mn=51300%2C+1100+Electric+Trimmer%2C+1981+%28SN+1000001-1999999%29

The thinner string works well in these machines and puts a lot less strain on them. I would suggest using a string of .065 range. The thicker (and more expensive) string used in the gas machines is too heavy for these lower powered electric units.

Look for a couple small windows on the sides of the center knob that sticks out, push in on these, they are tabs that hold the center knob on, after that the string bobbin should slip right out.

flooding out...change the air filter...

Onve you remove the cover the spool should pull straight out. Be careful, there's a spring under the spool that can fly out and get lost. You need that spring to re-assemble.

may have left handed treads on it

http://216.213.143.2/ProAuthor/ManProc.cfm?&sk=9C8C458D-4977-11DE-9261-00D0B789305D&&ProcID=9812&ManualID=301&ProductID=-1&Edit=No&Skill=1&Lang=-1