Hi. Simple thing to check out. If you have the wee round quick connect fuel line connector with the wee red tab that goes into the engine..they can be known to have the internal o ring seal perish very quickly (with the ethanol fuel these days). Happened to my 2016 115. Means they can draw air into the fuel. Then takes ages to bleed out the system. But what can also happen as a result or even alternatively, is the fuel pump in the FSM can fail. Either because of this..or even sometimes just because they can fail electrically. It should also be known that they can also have similar issues caused by lack of cooling to the fuel system fsm. You have the same engine as I do. Meaning that there is a cooling line fed off the top of the engine, that supplies the cooling to the fsm. There is a strainer in there that can get blocked up. Hope that helps.
Try getting a fuel pipe rigged up to the fuel fitting at the engine first off. To by pass and rule out the issue being the wee quick connect fitting that is now well known for failing these days. Then go from there. I’d also check for air at the shrader valve (where pressure gauge goes on the rail). When it is showing signs of the condition. That will tell you a story for sure. Will let you know if she’s drawing air from the fitting, fuel line or tank etc etc on the suction side. Good luck
