1976 Scamp fuel gauge problems

Okay, new sender is in, and it doesn't really do anything. From an empty tank, the gauge doesn't start to move until I have it about half full and then once it is full it's only reading 3/4 at best. Would this be caused by it being a new sender that isn't exactly like the old one is or could it be something else? On my meter, I see a nice sweep up and down the scale from 83ohms up to about 7ohms at the wiring behind the cluster.