Help with my singer

[xhmko]

Hi

I have recently bought a second hand singer
It is a made in brazil machine

i have found a manual on the internet that seems to work fine for it but when i start sewing, it does this weird thing where it sews fine and then misses a patch then sew fine again...can't figure it out.  i just end up with long bits of threadin between the stitching.

any ideas??