1976 evenrude 55 runs better when fuel tank is almost empty

by Chris
(St.Augustine FL)

I have a 1976 55 evenrude that runs great but won't go full speed until gas is almost empty. It gets on plane and is usable but when the tanks almost empty it will throw you back in your seat and skip along the water. Is this a air/fuel mixture problem adjustment or jets. Thanks in advance have been trying to figure this out for almost a year