Fuel filter drains

[OldBlueVolvo]

Hi all,


My car past its MoT recently. One advisory was for corroded fuel lines. I'm considering replacing them myself!


Also, the car has had a problem for quite a few years where the petrol disappears from the fuel filter after the car has not been used for a few days. The problem seems much worse now. I recently checked the filter the day after driving the car and it was already empty. I can't actually see any leaks.


Note that this car has the basic setup of Weber carburettor, mechanical fuel pump, and plastic fuel filter.


If I leave the car long enough it can take ages for the petrol to refill the fuel filter and for the car to start. I replaced the fuel pump earlier this year, thinking that the old one was duff.


I tried to measure the existing fuel lines (supply + return) using a micrometer. They measured as 8.8mm and 6.8mm, but the surface of the lines is quite rough.


Any thoughts on this? Any things to check other than the metal fuel lines?
I suppose that if I go ahead with replacing the lines, the first question will be what tubing to buy. So, what is the correct diameter? And what material is best?


From the original parts catalogue, the lines are 3.1m and 3.075m. Unfortunately NLA from Volvo.

[Forrest]

This is fairly common with carburettor and mechanical fuel pump set ups. They are not designed to retain fuel pressure or build it up prior to starting in the same way a modern fuel injected engine with electric fuel pumps does.

Minor leaks in the fuel lines will exacerbate starting issues. Think of it like trying to suck liquid through a straw with a hole in it. Minor leaks may not show up quite as readily as they would on a modern engine if they are letting air in prior to the fuel pump rather than leaking fuel out under pressure.

Is the Weber an after market replacement? I had one on a VW and found it to be unreliable so refurbished an OEM Pierburg to replace it. I don't think aftermarket Webers necessarily come properly set up with the correct jets and float settings for the vehicles they are sold for. If it's of any age you could check for internal leaks. You would need to buy an appropriate rebuild kit before taking it apart.

As for replacing the metal fuel lines this may appear daunting but if you are able to remove the originals intact you just copy the bends and joints to make up the new one. I did this recently with a hard brake line on a 940 and was very pleased with the result. Research beforehand the right metal and diameter of tubing to use and whether you will need to make any flared joints. If so, be aware that there are multiple types and you will need the correct tool for the type you need. Also get a proper tool for bending tube of the correct diameter as this will be more accurate and less likely to crush the tube than trying to bend it by hand.

Be wary of using copper tubing. This is rarely the right thing to use on cars as it is too soft and easily damaged. Copper-nickel is safer if you want something that won't corrode.