External fuel tank problem

[Spaddriver510]

My 2009 4hp 4 stroke will run fine on internal fuel tank but will not run on external fuel. The fuel cap is unvented.

[boats.net]

Be sure there are no air leaks between the engine and the fuel tank. Verify that your fuel pump is working properly.

[Spaddriver510]

checking fuel pump

Be sure there are no air leaks between the engine and the fuel tank. Verify that your fuel pump is working properly.

How do I verify the fuel pump is operating properly. Is the fuel pump operating when the engine is running on internal fuel tank?

[boats.net]

The internal tank is likely above the carburetor and can be gravity feeding the carburetor. remove the output like of the fuel pump and verify good amount of fuel at an adequate pressure.

[Spaddriver510]

Fuel filter

Any reason to check the fuel filter? Although the motor is a 2009, it has been run very little since it is on a sailboat.