Re: 18 hp merc.
Hi.
Could be the fuel pump, and it is a good idea to have the diapham and other replacement parts on hand as spares, and sometimes you need new parts when you take a pump apart because the old ones don't fit back in or don't look good. the motor could be sucking air into a fuel line someplace, but most of the time when you need to keep pumping the fuel by hand this problem is water or dirt in the filter(s). It usually pays to clean things out. You can dump out the fuel tank and see what was in there, Clean the filter at the pump, clean any other filters, loosen the machine screw on the bottom of the carb and let them drain and while they are draining pump fuel by hand with the primer bulb to flush everything. Be careful about fire!
I have had to do this quick fix lots of times, and found that when I have in line fuel filter problems one of the common reasons is that I keep refilling the same tank, or dumping dregs together, and the dirt and water accumulate until the motor gets a good shot.
Hope this helps.
