Re: fuel pump or primer bulb?
I am working on a similar problem with an older Mercury 650 (65 hp) outboard. Like yours, my primer bulb doesn't want to firm up, and though I can get the motor to run at low speed, it sounds like it's struggling to get enough fuel. It's relatively easy to start and the rooster tail is fine.
I cleaned the spark plugs, replaced the fuel tank, and the fuel line. I took apart the filter unit (it wasn't clogged) and cleaned it out. I also tried setting the fuel tank at different angles. This didn't seem to help the problem. The hose inside the new tank had fallen off, so I put a different one on (about 3' long). Still, the primer bulb won't firm up when the line is connected to the motor. Disconnect the line at the motor, and the bulb firms up nicely.
The consensus here seems to be that the fuel pump is bad. I'll do some more work and post again when I know more.