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Author Topic:   Air in Fuel Line

Frank O posted 03-29-2015 08:06 PM ET (US)
The old fuel-water separator for my OptiMax 250 was looking haggard (not to mention fused to its mounting bracket, which also looked ancient), so this weekend I installed a new filter-bracket. Per Mercury's instructions, I filled the new filter with fresh gasoline before screwing it on. While working on the connections, I also had to briefly disconnect the hose running from the fuel tank to the separator filter at both ends, in the process removing about 1/4-cup fuel from the hose.
After it was all back together, I pressed the primer bulb a couple of times and found that it became firm as usual. Should I be good to go? I'm just wondering if there could be air in the hose running from the tank to the filter.
jimh posted 03-30-2015 06:41 AM ET (US)
The squeezing of the primer bulb until it becomes firm is a good indication that the primer bulb has filled with fuel. If there were air in the fuel system it would probably have been pushed downstream from the primer bulb.
In outboard engines with a closed fuel system--I believe your Mercury OptiMax is such an outboard engine--there is typically some arrangement provided for venting the fuel system as a necessary means of operation. Air entrapped in the fuel line should be vented by the fuel system without further attention from you.
Consult the operator's guide (or owner's manual) for your specific engine to determine if any special procedure is needed during priming of the fuel system to remove air.
I am not familiar with your particular engine. I suspect the fuel system probably contains a fuel-vapor separator, usually some sort of a tank assembly. This component probably has a vent to release any vapor in the fuel system. Typically the vent is directed into the engine air induction system.
Frank O posted 04-03-2015 06:12 PM ET (US)
Thanks for the comments, Jim.
Today we got around to firing up the outboard for the first time following the installation of the new fuel-water separator. We ran the engine for several minutes in the slip. Interestingly, it ran fine for a few minutes, then died out. At this point, I felt the primer bulb and it was soft. After a few manual pumps it was firm, and we started up the engine again without incident.
I gather that there must have been an air pocket in the fuel line that gradually made its way down to the outboard. Hopefully that's the last of it, and the air is fully purged now.

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Author	Topic: Air in Fuel Line
Frank O	posted 03-29-2015 08:06 PM ET (US) The old fuel-water separator for my OptiMax 250 was looking haggard (not to mention fused to its mounting bracket, which also looked ancient), so this weekend I installed a new filter-bracket. Per Mercury's instructions, I filled the new filter with fresh gasoline before screwing it on. While working on the connections, I also had to briefly disconnect the hose running from the fuel tank to the separator filter at both ends, in the process removing about 1/4-cup fuel from the hose. After it was all back together, I pressed the primer bulb a couple of times and found that it became firm as usual. Should I be good to go? I'm just wondering if there could be air in the hose running from the tank to the filter.
jimh	posted 03-30-2015 06:41 AM ET (US) The squeezing of the primer bulb until it becomes firm is a good indication that the primer bulb has filled with fuel. If there were air in the fuel system it would probably have been pushed downstream from the primer bulb. In outboard engines with a closed fuel system--I believe your Mercury OptiMax is such an outboard engine--there is typically some arrangement provided for venting the fuel system as a necessary means of operation. Air entrapped in the fuel line should be vented by the fuel system without further attention from you. Consult the operator's guide (or owner's manual) for your specific engine to determine if any special procedure is needed during priming of the fuel system to remove air. I am not familiar with your particular engine. I suspect the fuel system probably contains a fuel-vapor separator, usually some sort of a tank assembly. This component probably has a vent to release any vapor in the fuel system. Typically the vent is directed into the engine air induction system.
Frank O	posted 04-03-2015 06:12 PM ET (US) Thanks for the comments, Jim. Today we got around to firing up the outboard for the first time following the installation of the new fuel-water separator. We ran the engine for several minutes in the slip. Interestingly, it ran fine for a few minutes, then died out. At this point, I felt the primer bulb and it was soft. After a few manual pumps it was firm, and we started up the engine again without incident. I gather that there must have been an air pocket in the fuel line that gradually made its way down to the outboard. Hopefully that's the last of it, and the air is fully purged now.