I just installed a used Merc. 850 (1973) on my boat (old 850>1974 lost compression on two cylinders but did not have a fuel delivery problem).

The new (used) engine fires on all cylinders and runs fine as long as I keep it primed with the prime bulb. I replaced the fuel pump with the one off of the old engine as it was working fine and have rebuilt the other fuel pump and still have the same problem, engine dies if I do not keep primed by hand.

As the engine does not have a pump rod as a car manual pump, I have no idea what operates the Merc. fuel pump.

Is their an electric pump that can replace the manual pump, or does someone know what is causing this condition!

thanks>> stormmn

check the fuel lines they are bad