My machine blanket stitch looks like a "V", not an "L"
When doing machine applique using the blanket stitch, some of my stitches make a "V". I have changed my needle. Could it have anything to do with using the wrong weight thread?
If some of your stitches are looking like V's instead of L's, you are experiencing skipped stitches.
You were absolutely correct in changing your needle first, as it's one of the most likely causes of this problem.
A skipped stitch happens when the thread doesn't make a loop in time for the shuttle to 'hook' it and twist the threads into a stitch. (You can see this is action by visiting my page Learn How Sewing Machines Work
and then scroll down to the first video...it really helped me understand skipped stitches.)
If the thread you are using is designed to be put through the needle of a sewing machine, then I suggest moving to the next largest size needle, so that the needle makes a hole big enough for the thread to pass through the fabric.
If the hole is too small, there'll be excessive drag on the thread which could definitely interfere with the loop forming at the proper time...and thus you see those pesky V's. Pretty much anything up to and including a 12 wt thread should be able to go through the needle of your sewing machine. (If the thread is thick you may need a 90 or even a 100 size Topstitching or Metafil needle.)
Anything bigger than that (meaning with a lower number...100 wt thread is very fine, 12 wt thread is thick...should be relegated to either the bobbin or for hand stitching.
I hope this has helped. I'd love to see what you're working on. When you're ready, feel free to submit a picture of your project on our Share Your Quilts
PS There's more information about skipped stitches Solving Your Sewing Machine Problems