I'm gonna agree with CCCC about the idle air circuit being gummed or plugged. The fuel pump on that motor sucks from the tank with a single hose, there is no pressure in the primer bulb and it won't stay hard when running. There is a U-Tube video explaining the idle circuit, with a diagram of how the air in that circuit pushes fuel into the carb at low speed. The timing linkage needs to be set precisely, as well. I have a 2004 60 hp and a factory manual, which covers the 70 and 90 also.
