When I sew, the bottom thread is bunched up in spots even though the top looks okay. What am I doing wrong?

You're either misthreading or not starting the seam correctly. Try the 10 minute fix... it'll catch both problems:





The 10 minute fix for most of what ails most sewing machines:


-- Dig out the manual. Take all the thread out of/off of the


machine. Pull the needleplate and the bobbin case if it's


removeable. Clean and oil per the manual's recommendation. Use a


brush and vacuum, not compressed air (which blows lint in


farther), and real sewing machine oil, not 3-in-1 type oil (it


hardens and freezes the machine) nor WD-40 type stuff (it's a


solvent, not a lubricant).





-- Put in a new needle of the correct point style for the fabric


you're sewing (ballpoint for knits, sharps for wovens) and the


right size for the thickness of fabric (10/70 for shirting weight


fabrics, 12/80 for heavy shirtings or light pantsweight. 14/90


for medium to heavy pantsweight, 16/100 for very heavy fabrics.


Make sure the needle is in right way around -- a needle in


backwards will skip stitches or not stitch at all.





-- Rethread, with manual in hand. Make sure the presser foot is


UP when you thread the top -- it opens the top tension so that


the thread actually gets in between the tension disk (loops on


the bottom, not enough tension on top).





-- Fetch up the bobbin thread. You need about a 4'; tail of thread


top and bottom. Run both threads under the presser foot and


behind it.





-- If you've been playing with the top tension, set it to 4. If


you've been playing with the bobbin tension, let me know and


we'll try to rebalance it, but you're likely to have to take it


into the shop.





Now, each and every time you start to sew a seam, this is how you


do it:


1) Place the fabric under the needle, and use the handwheel to


lower the needle into the fabric (be sure to turn it the right


way... seee the manual).





2) Drop the presser foot.





3) Hold the thread tails behind the presser foot with your left


hand.





4) Take a couple of stitches





5) Drop the thread tails and sew normally.