Scattymatty101

Gents. Having some issues with a mates Dt125 oil pump. Auto lube pump seems to be working on throttle but not on tick over, see video link. Note you can see it going up and down on throttle but not on tick over it sort of sits their in one position. Currently got a bottle hooked up with pre mix in until I solve this issue. Would air in the pump cause this? Thanks in advance