At that rate, it will do a litre in roughly 1 1/2 minutes. At 20l/100km this means it would take 30 minutes to pump 20l, and even flat out you won't get anywhere near 100km in 30 minutes, and you should get better economy than that, so the answer is, yes, that should be enough - but not by as large a margin as I would have expected.

The bubbles suggest an air leak somewhere, with pipe unions and the water trap bowl gasket on the pump being the main suspects, but it could be, for example, a small leak on the diaphragm of the pump. It is also likely to be exacerbated by any restriction in the supply line, typically the strainer on the fuel pickup being clogged.

John

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JDNSW
1986 110 County 3.9 diesel
1970 2a 109 2.25 petrol