On Fri, 16 Oct 2009 21:24:21 -0700 (PDT),
" wrote:

This machine most of the time ...
(...)
Also is there a more appropriate news group that I might try
that is dedicated to sewing machine repairs? Thanks, Lenny.
http://sewingforum.com
http://www.thesewingforum.co.uk

The top and bottom thread tension are the usual problem. My guess is
the bottom thread is adjusted too loose. It could also be the presser
foot misadjusted or tripping the thread. It might be the feed dogs
(under the foot) slipping or falling apart. Hard to tell without
seeing it in action.

See:
http://www.sewusa.com/Threading_Diagrams/Threading_Pages/Singer_Sewing_Machine_Threading/singer_513_threading_diagram.htm
Note the last photo on the bottom. If the bobbin thread doesn't pass
between the feed dogs and then towards the back of the machine, the
thread will probably bunch up.

Search Google for "sewing machine thread bunches":
http://answers.yahoo.com/question/index?qid=20080728180536AAogoPF
etc...

--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558