NEED INSTRUCTION SHEET FOR LINE INSTALLATION

Dave, I use the orange 2.4 mm .095" line, seems to give the best results. Check the attached links,manual,instruction and guides, Good luck
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http://www.stihlusa.com/WebContent/CMSFileLibrary/InstructionManuals/STIHL-FS-88-108-Owners-Instruction-Manual.pdf

How to Rewind Your Trimmer Head or Sharpen Metal Blades

HOW TO Stihl String Trimmer Head Replacement

Here ya go :) Maybe you could find manuals that can help you

http://www.manualslib.com/

check if you can download this instruction manual for a 26cc Icon grass trimmer. You have not provided the model number of your trimmer but generally it should be similar to this.
It requires 40:1 fuel to oil ration.
Do not worry if you cannot load this manual as I have already given the information.
Icon Line Trimmer ICPLT26 Operator Manual

There is a hole just above the grass trimming head that you can slip a screw driver into. Turn the head so that the inner and outer holes align where you can put a screw driver or other hard steel object in. Put it in there and then turn the head counter clock wise until it comes off, it may take a little effort to get it to move, but you should be able to do this with your hands. Once you get the trimmer head off, put the blade on and hopefully you still have the nut and washer accessories to hold the blade in place. You will need to place your screw driver back in the alignment hole to hold the head from spinning while you tighten the blade nut back down. Make sure it is tight, you don't want that blade coming off at ~10,000 rpm!

I bought a Shakespeare Push-n-Load 3 blade trimmer head at The Home Depot for about 26 dollars and picked up a pack of 12 replacement blades for another 7. Did a whole 3 acres worth of weed whacking and still didn't need to change the blades. I was also powering through some pretty thick bushes with ease. Highly recommended.

It sounds like that the automatic line release is damaged.

1. Remove and clean all debris from the head. I assume that you have already done this if you have changed the line a few times, but just make sure.

2. Remove the the head from the shaft.

3. There should be a large spring in there. If its broken, damaged or missing that will allow the head to spool line pretty fast. again make sure all debris is removed from this area.

4. Check the feed dogs in the same area as the spring. If they are worn the same problem will occur.

5. Install line on the spool.Make sure that it is wound the proper direction. There should be arrows indicating this. The line wound in reverse will also cause the same problem as well.

6. Put it all back together and see if works now.

7. If this doesn't solve it you may need to replace the head assembly.

Good luck!

Please download the Print Doc for this instruction manual and the detailed instructions for restringing the trimmer will be inside. Your model only had a parts diagram, but this model is the same. The download you want will be on the righthand side of this page.

http://servicenet.blackanddecker.com/Products/Detail?isId=true&productNumber=GH600&selectedType=7061#

You can find a complete trimmer head replacement at Hyperparts.com. Go into the Lookup By Application section and select the make and model of your trimmer to see a list of the heads they offer.

Hi,
I have the same trimmer and I fixed the problem for good by getting a shakespear line trimmer head to replace the original faulty design,it also has 4 line rather than 2 so it cuts better. It costs about $15.00
see link
http://www.lowes.com/lowes/lkn?action=productDetail&productId=120473-42694-14548&lpage=none&cm_mmc=search_yssp-_-Unassigned-_-060209-_-Shakespeare%20Universal%20Fixed%20Line%20Trimmer%20Head