Air leak in fuel line???? check out video

[bungholio]

https://www.youtube.com/watch?v=Iw3tM9IYhoU

2004 merc 5.0L 2bbl carb engine new fuel pump. In the video I tap a pressure gage into the fuel line before the fuel filter and fuel pump. I would expect there should be no air in the line. But you can clearly see there is a small flow of fuel but the hose is mostly full of air. This is on the low pressure intake side. Does this look normal or do I have an air leak. I tightened all connections, put liquid teflon on all joints, pulled gas tank intake tube and inspected for leaks. I can run the boat at full throttle and the tube fills up with more gas but always has air in it. This does not seem right?????

 

[bonzoscott]

Re: Air leak in fuel line???? check out video

It's just a bubble. Should eventually bleed. Did you run WOT for a while? Not sure liquid Teflon is the way to go. Should be all brass fittings.

 

[alldodge]

Re: Air leak in fuel line???? check out video

https://www.youtube.com/watch?v=Iw3tM9IYhoU

2004 merc 5.0L 2bbl carb engine new fuel pump. In the video I tap a pressure gage into the fuel line before the fuel filter and fuel pump. I would expect there should be no air in the line. But you can clearly see there is a small flow of fuel but the hose is mostly full of air. This is on the low pressure intake side. Does this look normal or do I have an air leak. I tightened all connections, put liquid teflon on all joints, pulled gas tank intake tube and inspected for leaks. I can run the boat at full throttle and the tube fills up with more gas but always has air in it. This does not seem right?????

I don't see an issue, your at idle and the pump is sucking fuel out of the tank. Once you on plane the air should be sucked out. When the engine is shut off the fuel solenoid will shut off and keep the line full, that is unless you have a leak at one of the barbed fittings.

Why would you put a pressure/vac gauge before the fuel pump? Having trouble getting enough fuel to the engine and thinking you may have a restriction?

 

[bungholio]

Re: Air leak in fuel line???? check out video

When I drive at full throttle the line fills up with more gas. But when I return to idle the air pocket is back.

I was looking for a restriction in the fuel line. I had a problem with the engine knocking at full throttle. Carb cleaner fixed this problem. I also did a rebuild on the carb. for good measure.

 

[bungholio]

Re: Air leak in fuel line???? check out video

Permatex? High Temperature Thread Sealant is the stuff I am using. I took the fuel shuttoff soelnoid apart and reapplied thread selant to the connections.

 

[alldodge]

Re: Air leak in fuel line???? check out video

Bypass the fuel shut off and see what happends

 

[bungholio]

Re: Air leak in fuel line???? check out video

Yeah I'm thinking about using a gas can and putting the tube in there to see if it has an air pocket too.

 

[alldodge]

Re: Air leak in fuel line???? check out video

Yeah I'm thinking about using a gas can and putting the tube in there to see if it has an air pocket too.

That will work but then your tank is above the engine some what. If you have an air leak the can may have it go away, but you still will not have found it. It is another place to start but in this case may induce other variables

 

[NHGuy]

Re: Air leak in fuel line???? check out video

If the line is not a major pain to reach why not just replace it? If someone hacked the install or bumped the line it could be cracked allowing a little air in there.
I did fuel line in my boat when it was 20 years old. I did it because I am fussy about stuff and it was brittle.
This was my second year with the boat. I also did wires, cap and rotor so I can't say for sure what helped most, but the next season I had no more lean pop under load.

 

[gm280]

Re: Air leak in fuel line???? check out video

I see the same issue on my lawn mower in the clear fuel filter as well. But gas is reaching the carb or it would not be running. Not a problem in my opinion... And if you want to see fuel pressure, you need to install the pressure gauge after the pump. But I think you already know that.