Classic cars forum & vehicle restoration.

[Ray White]

I always say you don't know what you don't know. I realise now that I have made an elementary mistake when fitting a fuel filter to my MG TC. I thought it would fit nicely to the outside of the battery box on the bulkhead so early on in the build, I went ahead and inserted the filter into the fuel line; after the pump and before the carburettor.



What I should have done, apparently, is locate the filter before the pump.

I have read that the reason why you don't want the filter between the pump and the carb is that
the pump is constantly trying to pressurise air in the filter and constant pressure on the float valve will cause it to leak and run rich. It can also cause problems when setting up the carb.


I had wondered why the float chamber tended to leak ...and now I know.

Hopefully my experience with this will be of some value to anyone else who didn't think it mattered where the filter was located...and hopefully avoid making the same mistake that I made.


I shall now have to move the filter to a suitable position before the pump and restore the direct line from the pump to the carb.

[alastairq]

I have both...before & after.
Don't have bother with leaks on the twin SU's.

Not long ago , Halfords [remember them?]... had an 'offer' on Crosland fuel filters which were actually specific to my Suzuki Not-so-very-Grand{!} Vitara, 2 litre petrol.

It is located at the rear, near the tank, but after the fuel pump.
OK, so the 'thing' is fuel injected, so 'high pressure'...and there are 'returns,' etc.
But the metal filters [a can, really] were nearly half the price of decent plastic inline filters...so I got a couple..[on a pension, needs must, etc etc?}
They have a side 'input' and a top 'output,' are fairly compact, so fitted onto the Dellow's bulkhead quite nicely.
Being a can, it is mounted vertically[on both the Suzuki, [a 2001/2 model] and on the Dellow..and, aside from rusting{?} won't be as prone to 'splitting' as the plastic filters when under 'pressure!'

I'm not so sure about this 'issue' of positioning of filters re-the pump?

I've never had the leaky carb issue.
What I do find concerning is when a plastic [AKA cheapoh?] fuel filter is mounted near the carb, but also near stuff that gets very hot, like exhausts?
If the plastic casing splits, guess where the fuel might end up?

In the past [Yup, I have a past!]...I have placed plastic filters after the pump location, but well down the side of the engine bay, a long way from anything hot....without issue at the carb[s]

The idea of the pump 'pressuring' the air in the filter if mounted after the pump really is at odds with one manufacturer of filters...and fuel pressure regulators!
Namely, Malpassi?
Commonly known as 'Filter King!'

The Filter King fuel filters also contain the fuel pressure regulator, so must be mounted between the pump and the carb[s]!

If an after-pump filter is going to create issues at the carb float chambers....why doesn't it do that with a Filter King mounted correctly?

I would ''suggest''....[if I dare, in such august company?]...also fitting a [Malpassi??] fuel pressure regulator....They do look rather nice, and would prevent over-pressure fuel supply, which can happen with a lot of electric fuel pumps used with carbs.
[Or, fit a small bore fuel return pipe back to the tank area...tee'd off the main fuel line at the carb? Then the carb simply draws what it needs?

Might also offset hot starting/fuel issues with today's petrol which vanishes rather more quickly than I'd like.
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

[Ray White]

Thank you Alastair for such a thoughtful response. I like the idea of a return pipe to the tank. It is a nice traditional solution and wouldn't look out of place under the bonnet,,, though I am unsure how I would attach the end to the tank.(Remember, it is all exposed...)

AS it happens I would be new to Malpassi fuel filters and regulators and (in all honesty) a bit out of my comfort zone ...but I am willing to give it a try.

[alastairq]

https://www.burtonpower.com/parts-by-category/fuel-system/fuel-regulators-filters-carb.html?srsltid=AfmBOoo0ABPr7t0HXiYbcYyqNGuVI1akT60BPNTZmw6cKU61pwZKOiYW


https://www.glencoeltd.co.uk/malpassi-carburettor-pressure-regulators/malpassi-filter-king-fuel-pressure-regulators/


Hi Ray, I included but a couple of retailers, although I haven't been a customer.
Just plucked off Google.

The filters for the Filter King are replaceable, thus perhaps offsetting the initial cost for the unit?

They are quite substantial bits of kit, so would look quite purposeful under the MG bonnet. A little less insubstantial than a plastic filter, etc?

Also, the fittings are all proper screw in items...

Also available from the likes of Demon Tweeks...


A return pipe to the tank can be as simple as, letting it into the tank filler tube, if there is one?
_________________
Dellow Mk2, 1951 built, reg 1952.
Fiat 126 BIS
Cannon special [1996 registered. Built in 1950's]
----------------------------------------------
Ford Pop chassis, Ashley 1172 bodyshell, in pieces.

[Ray White]

[MikeEdwards]

I also have fuel pump into fuel pressure regulator into fuel filter without any noticeable issues. There is a sort-of filter in the tank, in the shape of a gauze "sock" that fits over the end of the pick-up pipe.
_________________
1976 Vauxhall HP Firenza, 1976 Vauxhall Sportshatch (x2), 1986 Audi coupe quattro, 2000 Audi TT

[Ray White]

[Keith D]

On my Austin A40 I have blanked out the engine block where the 'correct' mechanical fuel pump was fitted and have installed a low pressure SU pump on the firewall. I have fitted a plastic in-line Ryco filter between the tank and the pump. This has been 100% satisfactory. No problems at all (apart from the annoying rattle when the ignition is first switched on!)

On my '26 Chrysler I fitted an in-line plastic Ryco filter between the fuel tank and the firewall mounted Autovac tank. I was concerned that the filter would impede the flow of petrol to the Autovac tank as this is operated by engine
vacuum from a low compression engine. But again, no problems whatsoever.

I replace these filters (worth around $20 - about 10 pounds in your money) every year or so, depending on the cars annual mileage.

Keith
_________________
1926 Chrysler 60 tourer
1932 Austin Seven RN long wheelbase box sedan
1950 Austin A40 tourer
1999 BMW Z3
Its weird being the same age as old people.
You are either part of the problem or part of the solution

[Ray White]

Hi Keith. Talking about A series engines, when I replaced my Austin A30 803cc engine with a 1098 unit from a late Farina A40. I had to convert from the original mechanical fuel pump to an electric one.

I learned a lot about petrol pumps from that experience. There are as you probably know 'pushers' - like the Austin/Morris 1100 (ADO16) used - that were mounted in the boot and "pullers" like the Morris Minor ones that sit on the bulkhead.

I also found to my cost that you can't use a high pressure pump where a low pressure one is required.!!

Back then, at the age of 19, I had a lot to learn... but fortunately my Dad was always on hand to set me straight....

Happy days.

[MikeEdwards]

[Miken]

I have read that the reason why you don't want the filter between the pump and the carb is that
the pump is constantly trying to pressurise air in the filter and constant pressure on the float valve will cause it to leak and run rich.


If you fit a Viton rubber float valve (available from Burlen ) wouldn't that solve any leakage problems?

[Ray White]

[bjacko]

I am wondering why there is air in the fuel filter, surely it should be full of fuel?
_________________
1938 Morris 8 Ser II Coupe Utility (Pickup)
1985 Rover SD1 VDP

[MikeEdwards]

[Ray White]