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Bubbles (and partially filled filter) are normal. You would have to isolate the line(s) and run a vacuum test to ascertain they are air tight. Vapor lock happens on the suction side of the fuel pump. Fuel percolation is the evaporation of fuel in the carb bowls/inlet line if there is significant heat soak.
Simply so, should a fuel filter have air in it?
A fuel filter is going to have air in it unless you can bleed it. It starts out with air and then fills up. You can do a lot of parts changing or you can see if the problem is really what you think it is or something all together different.
Consequently, how do you get air bubbles out of fuel lines?
How to Bleed a Gasoline Line
- Fill up the gas tank with fuel.
- Start the engine but do not allow air into the system. Have a friend turn the key in the ignition to “Start” for approximately 3 seconds.
- Allocate approximately 20 minutes for the engine to sit if flooding occurs while bleeding the fuel lines.
Air bubbles in a fuel line can lead to stalling, hiccuping or refusal to start. Keep your fuel lines free of air to help keep your car running smoothly.