The lines should be changed once a year or when they stiffen. Routing the fuel lines is very essential. Then, the protected line is tied to the frame or other parts of the engine. If fuel filters are used, they should be as small as possible but big enough not to restrict the fuel flow. Great care must be taken so they are completely filled with fuel.
Any air pockets can cause a lean mixture or engine hesitation at high power settings.
They should be always installed in a vertical position to eliminate all the air. Small conical fuel filter installed in vertical position will not cause vapor lock. Bigger fuel filters will be more difficult to fill completely and may cause the above-described symptoms. If they are higher than the fuel tank, after the engine is stopped, the increased weight of the fuel inside the big filter can siphon the fuel back into the tank, making a restart very difficult. If bigger filters are used, it is a good idea to install a check valve under them to prevent the siphoning action.