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Air in fuel filter

Dave the tram

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I have a transparent fuel filter,between tank and pump, just before tthe pump. Should it have air in it. Sometimes it's full, sometimes part air, and occasionally empty but fills when running engine. Is this right?

I'm assuming it's air, no reason for vapourisation as its not hot and near the bulkhead. If it's air, where does it come from? I wonder if I've got a leaky joint or a blockage so that it can't pull fuel through fast enough.

Any ideas?


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I have the exactlly the same sort if filter on car and also on 2 lawn mowers with gravity feed fuel lines.

the appearance is the same as your pic re varying amount of filter that appears empty of fuel

-and they are running ok

On one unusually hot day last year mower conked out. Filter looked empty.1/2 hour later, fuel in filter -started fine.

so ?? degree of vapourisation occurring - but dont know really.


If it wasnt transparent you wouldnt know...

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Wondering about this (mounted near vertical). Never really looked at filter after running, though it is only about 1/4 (max) full generally.


Squirts what I thought is a healthy amount out of fuel line when cranking.


Any advice great thanks.


Cheers, Dave

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If you get any bubbles entering the filter then you are sucking air from a leaky joint or hose between filter and pump


if there is just a void /air gap in the filter ,,, dont worry about it its fine your output to the carbs is

a good squirt then all happy and smiling

Think about your modern it has a solid metal canister filter , you cant see whats going on and hence cant worry about it


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