singer 201k will not sew or drops stitches?

I am new to sewing and sewing machines but I have just bought a couple of old singer sewing machines a 99k which I paid £10 for which I have managed to get working with a new foot pedal, but it wasn't quite heavy enough for what I needed it for. I then managed to buy an old 201k which seems to be in very good condition for less than £7 ! it even has the old style 2 round pin electrical plug on it. However I had a bit of a job to get it to thread the bottom thread as it just didn't want to pull through the needle hole. once it did pick it up, I tried to sew with it, however it either sews without catching the bottom thread or sews correctly with a stitch once every 8 - 10 times the needle enters the material. Could it be the timing is incorrect ? if so how do I adjust it ? or what else could be wrong ? The machine is threaded correctly. Many thanks in advance Steve