Question.! ..anyone know if by using a electric fuel pump on a Yanmar 3Jh3e, in line for bleeding and as a standby in case of mechanical failure, with a 5-7 PSI rating could hurt the diaphragm on the mechanical pump. Some have suggested that this could cause fuel in crankcase. A 2-4.5 PSI pump is available at a much higher cost and delivery time will keep me dockside yet another week. Am anxious to troll-sail for Rockfish in the Chesapeake while the wife is in good humor and busy with the girls.!!!
On my Yanmar 3gmd (it also has a low pressure mechanical engine mounted pump) I installed a hand primer bulb (one you would use on a gas outboard engine). I pump the bulb to prime the engine (actually put a fuel line that connects to the fuel return from the engine with valves so I can prime the entire line without having to catch the fuel in a bucket). If the mech fuel pump stops working I might be able to use the fuel bulb to pump fuel to the engine.
I would be hesisant to use an electric fuel pump as it could send fuel into the engine if the mech fuel pump diaphram breaks. Also, in case of fuel leak it would fill your boat with diesel. I would carry (and I do, a spare mech fuel pump).
However, a lot of people do use an electric pump for priming their engines.