Sewing Machine Zig-zag Tension

Question

My Singer Capri had been 'got at' before I bought it second-hand.It did not pick up the bobbin thread.I have worked on it and now can pick up the bobbin thread but the zig-zag is wierd; there are loops on both sides of the cloth, one row on each side, as though the tension is not correct.I would very much like to get the details for setting the bobbin-hook timing, please.I am finding out about the mechanics of the machine when I really just wanted to make kites for the grandchildren [? & me].Stephen