Illustration of poulan weedeater cutting head

have you cleaned all the grass and grit out of the entire head? Some times it will get gritty and sticky and not release Line when it gets low on line

Here is the info from the manual, the replacement line is put in near the center of the spool on the top of it, you simply feed it in. I have included a link to the manual so you can see the pictures. Look at page 10 for these instructions.
http://www.weedeater.com/ddoc/WEEO/WEEO2009_USen/WEEO2009_USen_TE475-952711797_545186833.pdf
LINE REPLACEMENT Pre--wound spools offer the most convenient method for replacing line and ensuring optimum performance. S Replacement spools are color--coded to ensure use of the correct spool with your unit. Be sure to use the same color spool as the existing spool. NOTE: Always clear dirt and debris from cutting head components when performing any type of maintenance. S Hold spool and unscrew cap by turning in the direction shown on top of the cap. S Remove line guide ring and spool. NOTE:When removing and/or installing spool, ensure dust cup remains installed over shaft. Use a pre--wound spool or refill spool with line. If using a pre--wound spool, remove tape strip from line and spool. REFILLING THE SPOOL WITH LINE WARNING: Use only 0.080" (2 mm) diameter round line. Other sizes and shapes of line will not advance properly and will result in improper cutting head function or can cause serious injury. Do not use other materials such as wire, string, rope, etc. Wire can break off during cutting and become a dangerous missile that can cause serious injury. 1. Cut a length of 25 feet of 0.080" (2 mm) diameter round WEED EATER brand line. Feed line in direction shown on spool. Spool 2. Insert one end of line into center cavity of empty spool. Ensure line will feed into spool in the direction shown on the spool (counterclockwise). 3. Continue feeding line into spool, leaving 4 -- 6 inches (10 -- 15 cm) unwound from center of spoo

Here is the info from the manual, the replacement line is put in near the center of the spool on the top of it, you simply feed it in. I have included a link to the manual so you can see the pictures. Look at page 10 for these instructions.
http://www.weedeater.com/ddoc/WEEO/WEEO2009_USen/WEEO2009_USen_TE475-952711797_545186833.pdf
LINE REPLACEMENT Pre--wound spools offer the most convenient method for replacing line and ensuring optimum performance. S Replacement spools are color--coded to ensure use of the correct spool with your unit. Be sure to use the same color spool as the existing spool. NOTE: Always clear dirt and debris from cutting head components when performing any type of maintenance. S Hold spool and unscrew cap by turning in the direction shown on top of the cap. S Remove line guide ring and spool. NOTE:When removing and/or installing spool, ensure dust cup remains installed over shaft. Use a pre--wound spool or refill spool with line. If using a pre--wound spool, remove tape strip from line and spool. REFILLING THE SPOOL WITH LINE WARNING: Use only 0.080" (2 mm) diameter round line. Other sizes and shapes of line will not advance properly and will result in improper cutting head function or can cause serious injury. Do not use other materials such as wire, string, rope, etc. Wire can break off during cutting and become a dangerous missile that can cause serious injury. 1. Cut a length of 25 feet of 0.080" (2 mm) diameter round WEED EATER brand line. Feed line in direction shown on spool. Spool 2. Insert one end of line into center cavity of empty spool. Ensure line will feed into spool in the direction shown on the spool (counterclockwise). 3. Continue feeding line into spool, leaving 4 -- 6 inches (10 -- 15 cm) unwound from center of spool

Hi and welcome to FixYa, I am Kelly (almost old at 56)
I looked up your parts and have come to the conclusion that you have items 13, 14 and 15 of this link:
http://www.ereplacementparts.com/images/poulan/RT112_.pdf

Watch the video in this link:
http://www.ehow.com/video_4426520_learn-spool-weed-eater.html
it should help you.

I found the manual here:
http://lawnandgarden.manualsonline.com/manuals/mfg/weed_eater/rt110_rt112.html

SEE PAGE 7 of the above manual. Includes pictures. Try pressing in and rotating the spool to remove it.

1. Disconnect the unit from the power

source.

2. Remove the spool by firmly pulling on the

tap button.

3. Clean entire surface of hub and spool.

4. Replace with a pre-wound spool or cut a

length of 30 feet of 0.065! (1.65 mm) diameter

Weed Eaterr brand line. Use of

heavier lines could overload and damage

unit.

WARNING: Never use wire, rope,

string, etc., which can break off and become a

dangerous missile.

5. Insert one end of the line about 1/2 inch (1

cm) into the small hole inside the spool.

6. Wind the line evenly and tightly onto the

spool. Wind in the direction of the arrow

found on the spool.

7. Push the line into the notch, leaving 3 to 5

inches (7 -- 12 cm) unwound.

8. Insert the line into the exit hole in the hub

as shown in the illustration.

9. Align the notch with the line exit hole.

10. Push the spool into the hub until it snaps
into place.

11. Pull on the line extending outside the hub

to release it from the notch; otherwise, the
unit will not function properly.

Thanks for choosing FixYa,
Kelly

weedeater hard to start

Pull on the tap head. Straight out. Hard. Here's the Weedeater manual. http://72.3.225.179/manuals/545117522e.pdf The spool should just pull out, its held in by 2 clips, royate it till it pops up then pull it out, with a wiggling motion, Grasp firmly and pull straight out....per tech support from 800 number on machine.

ignition coil,or blown head gasket...

There are five ways to change trimmer line depending upon the style of trimmer head on your unit.

The first style has a locking tab on the side of the trimmer head that must be depressed while the lock ring is turned counter-clockwise. This will remove the cover and give access to the spool which can then be pulled out, rewound with the line (winding in the direction of the arrows on the spool), and re-installed.

The second style requires lining up the marks on the bottom of the spool tap/button assembly and firmly pulling straight out on the tap button. This pulls the spool assembly out so it can be re-wound and inserted back into the hub assembly.

The third style requires pushing in and down on the two locking tabs on the side of the trimmer head. This will remove the cover and give you access to the spool.

The fourth style of trimmer head is the Centrex. Remove the cap on the bottom of the head by unscrewing it. Remove the guide ring and remove the spool from the unit. Cut a 25ft length of line and insert one end into the center cavity of the empty spool. Feed the line into the spool, leaving 4-6 inches unwound from the center of the spool. Reinstall the spool, guide and cap, making sure the notch in the guide is facing away from the spool and the line is in the notch.

The fifth style is the fixed line cutting head. This style cutting head uses a pre-cut piece of cutting line. After removing the worn line from the cutting head, insert the precut piece into the positioning tunnel leaving an equal amount out each side of the tunnel. The ends of the line can then be inserted through the exit tunnels.

Pull the spool straight off of the machine. There are arrows on the bottom of the spool indicating the winding direction. Also, there are holes in the spool. Place the line in the hole just enough to hold it while you are winding the line. Not too far, say 1/8".
Wind the outer spool first, and put the end in the notch when the spool is full. Leave about a 6" tail and cut the line. Now wind the inner spool, and place the line in the notch that is 180 degrees from the first line's notch. Leave about a 6" tail, and cut this line off. Now, turn the spool toward the machine. While holding the spool, thread both tails of line through the grommets on the machine head, and work the spool onto the head. The tails should feed out the grommets as you do this. Seat the spool, you'll feel it click into place. Tug on the ends of the line to pull the line out of the notches. You're done!
Best regards, --W/D-- please feel free to rate this carefully hand-crafted solution! --thanx!--

if its the newer type all you need to do is grab the black knob at the bottom of the trimmer head and pull it carefully straight towards you and it should pop off
wind line on the spool in the direction the arrow shows you there is a small hole you put the line in to start the line before you wind it it is labeled .065 or .080
wind about 10-15 feet of either .065 line or .080 line and lock the line in at the edge of the spool and thread the excess thru the hole and push spool back on and pull each line until it unhooks from where you locked it in .
this is the directions to the weedeater heads and spools mostly used on this product.

if its two lines then pull out 20 feet of new line cut it and put the two cut ends side by side and insert the cut ends into their respective holes in the spool and wind in the direction of the arrow until you wind to the loop then cut the loop lock your lines into place and thread it thru both holes keeping the lines kind of tight and push the spool onto the housing as it snaps in pull each line to unlock it from where they were held so the bump feed will work.

hope this helps you