"hose hooked to the riser?" What does that mean? You shouldn't be connecting a hose directly, but rather using a bucket of water for the pump inlet. The vane pumps can pick up only a few feet of head and should self prime.
What pump? You could have a Sherwood or an Oberdorfer. If it's the latter, check the faceplate - it needs to be smooth. The inside of the faceplates gets gouged over time and either need to be replaced or serviced to flat.
Stu Jackson, C34, 1986, M25 engine, Rocna 10 (22#)