Check the lines
Hi, there,
looks like either air getting somewhere in the line or a bad pump. I would first check the pump, because it is less hassle and old pumps are known to have issues. In my case, the air was actually leaking through the screw-on strainer.
Test the pump directly with a bucket of water - put one end of the piece of the hose in the bucket, and the other on the intake barb (may have to have a fitting for that) of the pump. If the flow is steady - well, partner, you are in for some fun with lines. Loren had a lot of information in earlier threads on thsi subject.
Good luck!
Stanly