Evinrude outboard fuel problems 1977 70hp

I have a 1977 Evinrude 70 horse outboard. The problem I'm having is it runs fine for awhile then it will act like it's running out of gas and it collapses the siphon bulb. I have changed tanks, the siphon bulb, and the fittings and it still does it. Could it be the fuel pump going bad? It's not overheating according to the heat gauge. If I have someone pumping the bulb, it resumes full speed for a short time, and then collapses the siphon bulb again. I loosed the caps on the gas tank thinking that it may be creating a vacuum, but it still does it. Does anyone have any ideas as to what it might be?

Re: Evinrude outboard fuel problems

if it's sucking the bulb flat, the fuel pump is good, some problem outside the motor.
try another 6 gal tank and another hose and bulb. let us know.