2003 40 HP Mercury EFI Outboard fuel issue

[MBTracker]

Hello, I'm seeking help before I go down the rabbit hole. I'm having a fuel issue on my motor. It starts up fine but when I start to go full throttle it wants to bog down and die. After a couple of tries, it will run with no issue then wants to seem like it wants to die again. Stop for a few minutes prime the bulb again and we are off with no issues. After 30 minutes to an hour of fishing, it starts over again. I checked the gas tank and there was no water in the system. I replaced the primer bulb/ gas line/ both filters/ spark plugs. At home, it ran fine. I get to the lake same issue.  The difference is the primer bulb would stay flat, I would need to message it to get it back round again then squeeze again a few times. Sometimes it would work then other times it wouldn't. I would need to disconnect the male/female from the gas tank to the motor let the gas out of the line then prime again and it would run fine until I turned off the motor.
Seeing as this is a new primer bulb ( not OEM part ) could this be the issue or could I have an issue with the male/female connection from the tank to the motor?

[Donald Garner]

Here's a video explaining some issues and checks that could help you fix your problem.




Hope this helps and good luck on getting your outboard operational.

[Mike Cork]

A couple things I've seen before...

Mud dobber clogged the vent port.

In tank fuel filter blockage

Fuel pump on the motor. On smaller motors, the fuel pump is actuated by compression off a cylinder. The diaphragm that separates this pressure from the fuel can crack or get a small hole in it and cause all kinds of intermittent and changing fuel problems.

Disclaimer, I'm no mechanic, just experienced at shot gun maintenance on various motors...

[MBTracker]

Hello Mike thanks for the info. I recently changed the fuel pump as well and got the same issue. I have noticed that I have to release the pressure from the fuel line quick disconnect, and then re-prime the bulb. and it will run fine.  On land, I have no issues. 

[Princeton_Man]

Hello Mike thanks for the info. I recently changed the fuel pump as well and got the same issue. I have noticed that I have to release the pressure from the fuel line quick disconnect, and then re-prime the bulb. and it will run fine.  On land, I have no issues. 

There's an obstruction of some kind. If you can simulate the both the motor's and tank's exact position/angles on land, as if it's in the water, it will probably do the same thing. Can you borrow a tank with the Merc fuel line coupler from the dealer or a marina? You might try replacing the fuel coupling on the motor, there may be a screen in that as well.