I have loops extending over the edge of the fabric. I have turned the stitch width knob as far to W as possible but still have overhanging loops? Please help.

The stitch width should adjust up to at least 1/4" wide. When doing applique, set the machine so the needle is centered on the raw edge of the fabric. If your machine is not stitching wide enough to cover the raw edge, then perhaps something is amiss with the machine. May need to take it for service.

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You can download a manual from this link
http://www.singerco.com/uploads/download/664_14u34b,234b.pdf

Check page 16, changing the seam width is done by moving the cutting blade left or right and using only one needle. So if you want the narrowest seam, use the right needle only, remove the left one, and move the blade as far left as you can. Your manual says to turn machine off at the wall for safety, many overlockers will have a motor cutout when you open the front covers, but its good practice to turn off too. Then you put pressure against the upper moveable blade and swing it up out of the way and make adjustment to the lower fixed blade with a screwdriver in your kit (some overlockers it is a knob you move to move the blade position).

And reverse for a wide stitch, use left needle for 3 thread wide seam, and move the blade far right.

You can also use the 4 thread seam where you use both needles and trim up narrow but the seam will be heavier than a three thread.

Each time you make changes to the amount of fabric being trimmed, you may need to finess the upper and lower looper tensions to ensure the seam is tensioned enough to just meet on the cut edge of the fabric. This is the norm for overlockers, each fabric will behave a little differently so you need to test stitch and adjust a little. Your manual will explain this process too.

Possibly you need to adjust the knife. It sounds like the knife is positioned too far to the right which is causing the cut fabric to extend further than the edge of the stitching. The thread chain is probably so tight against the edge of the fabric that it is folding it over.Move the knife a little to the left and try it again. If the thread chain is hanging past the cut fabric then the knife was moved too far to the left.

You move the top blade to the right to trim less so stitch forms wider and use left needle. Or both needles for 4thread seam which is more for knits. Blade has a knob usually to adjust it's position. You should test on scraps of your fabric as the weight of the fabric will also determine width of the seam. Adjust top and bottom looper tensions to encase cut edge neatly.

you don't say what make and model serger this is.

However, as a rule of thumb, set the blade to widest setting, then test serge and tighten up the top and bottom looper threads to encase the cut edge neatly. So you would need to turn the dials on the two right hand knobs to a higher number, just move each dial one number at a time and test serge again.

The other possibility is that the thread is not between the tension discs properly, so check your thread paths, when you pull on the thread below the tension dial, it should feel firm to pull.

I always test serge scraps when sewing a new fabric and adjust the tensions to suit it before beginning a new project as a lightweight fabric will behave differently to a heavy fabric.

I have the same model, have you turned the first knob on left, the stitch selector, to the stitch you want? Then turn the middle knob, the stitch width to "4". Use the colour guide marks shown in the little picture on left of the knobs so you are dialing up the right settings. So for the zig zag, elastic blind hem, scallop, overcasting and multi-stretch stiches, 1-6 on the diagram you'll be setting the left knob to 1, 2, 3, 4, 5 and 6 respectively and the stitch width and length knobs to "green", you can vary the length and width to suit what you want.

Then for the cams, you need to set everything zero, turn stitch selector to 7, the cam setting. then turn the width to orange again (3-4) and the stitch lenth selector to the orange setting, right around the knob. This engages the "Elnagraph" the device under the flap on top of the machine to read the discs. Basically the green stitches the needle is swinging from side to side while the feed dogs move the fabric forward, making your zig zags, blind hems etc.
But when you engage the Elna graph, the machine matches stiches by moving the fabric "forward and backwards at certain times, while the needle does its thing from side to side. This is what makes elastic or stretchy type stitches because you are putting "stretch" into the seam by sewing forwards and backwards.

Please note: always turn your stitch width and length back to Zero BEFORE you make any changes to the left knob and select a new stitch as this saves on wear and tear to the moving parts in these wonderful machines.

I do hope this assists you and I haven't just told you stuff you already knew!

I have the same model, have you turned the first knob on left, the stitch selector, to the stitch you want? Then turn the middle knob, the stitch width to "4". Use the colour guide marks shown in the little picture on left of the knobs so you are dialing up the right settings. So for the zig zag, elastic blind hem, scallop, overcasting and multi-stretch stiches, 1-6 on the diagram you'll be setting the left knob to 1, 2, 3, 4, 5 and 6 respectively and the stitch width and length knobs to "green", you can vary the length and width to suit what you want.

Then for the cams, you need to set everything zero, turn stitch selector to 7, the cam setting. then turn the width to orange again (3-4) and the stitch lenth selector to the orange setting, right around the knob. This engages the "Elnagraph" the device under the flap on top of the machine to read the discs. Basically the green stitches the needle is swinging from side to side while the feed dogs move the fabric forward, making your zig zags, blind hems etc.
But when you engage the Elna graph, the machine matches stiches by moving the fabric "forward and backwards at certain times, while the needle does its thing from side to side. This is what makes elastic or stretchy type stitches because you are putting "stretch" into the seam by sewing forwards and backwards.

Please note: always turn your stitch width and length back to Zero BEFORE you make any changes to the left knob and select a new stitch as this saves on wear and tear to the moving parts in these wonderful machines.

I do hope this assists you and I haven't just told you stuff you already knew!

It has nothing to do with threading it wrong. Just decrease your stitch width and this should solve your problem.

there are generally two variable controls .. one adjusts the stitch length (distance between stitches measured in stitches per inch) ... the second is stitch width .. that adjusts how far the zigzag moves left and right .. thats usually just a number from 0 to 10 or so .. 10 would be maximum width .. 0 would be used for straight stitch ..
so you need to adjust the stitch width control to make the stitching narrower .. the controls are called different things on different brand sewing machines .. if you have the brand and model number then there may be instruction booklets available ...

There are 3 things that come to mind for me.  I should say that I have a Bernina 1300DC, so your machine may not have the same parts, but check these things.  First, are you using 3 threads?  If so, is your needle in the narrowest setting, in the right hand hole closest to the body of the serger? Secondly, is your rolled edge lever retracted?  This lever is attached to a wide tooth that holds the width of the seam in place.  It is under the presser foot, between the loopers, and should retracted so that the stitches are allowed to become narrow.  If your machine doesn't have this lever, don't worry, you can also try a third thing.  Adjust your cutting width to a narrow setting.  There should be a knob that moves the upper cutting knife from right to left-- right being a wider seam, leaving more of the fabric intact, and left making a narrower seam that trims off more of the fabric as you sew. 
Hope this helps! Elsje