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Inline filter BEFORE or AFTER pump

thspeller

In Fourth Gear
I have a 2.25 petrol with Weber carb - it’s prone to blockage so needs an inline filter. The manual says fit just before carb but I’ve had lots of feedback that a plastic inline filter directly over the hot exhaust manifold is a bad idea. As a compromise, is there any reason why the filter couldn’t go between the tank uplift and the pump instead? Thanks Tom
 
I have a 2.25 petrol with Weber carb - it’s prone to blockage so needs an inline filter. The manual says fit just before carb but I’ve had lots of feedback that a plastic inline filter directly over the hot exhaust manifold is a bad idea. As a compromise, is there any reason why the filter couldn’t go between the tank uplift and the pump instead? Thanks Tom


Or you can buy a pump with a filter bowl attached.

 
If the intention is to filter crap that may originate in the fuel tank, then it shouldnt (theoretically) matter where in the fuel line it goes..?
The only way that I can think it would make any difference is if the filter became partially obstructed, in which case the pump may find it easier to 'push' fuel through the filter than to 'pull' it through...
 
Years ago when all performance cars had Weber or Dellorto carbs, it was quite common to fit a combined fuel filter and pressure regulator so that the electric pump didn't defeat the float needle and cause the level to vary.
If I had an electric pump and Weber I would be inclined to fit a good quality filter and regulator on the bulkhead, those cheap plastic inline filters are not the best.
 
On the efi models there is a gauze filter in the tank, before the pump and a cartridge type filter on top of the chassis.
I am trying to remember how the factory pump and filter are arranged on mine which has both of them mounted on the chassis.
I know the filter element has to be changed every 12,000 miles and I wash out the gauze filter inside the pump body each time I change the paper element.
This is the filter.
And this is the element for it.
 
I've got a weber 32/34DMTL carb , and have a glass filter bowl on the mechanical lift pump and a cheapie plastic filter mounted same side as dizzy near the front of the engine.
If I went to an electric pump I would fit the swirl pot on the bulkhead as that should remove vapour and dump extra back to to the tank.
The glass bowl seems to catch a lot of sand, but virtually nothing in the inline filter. The carb itself has a gauze filter anyway.
 
Despite seeming illogical, most oem setups filter the fuel AFTER the pump.

My series 3 with glass sediment bowl is, my ninety with facet redtop was after, my other fuel injected cars are after

I wonder why?

Maybe because pumps are quite robust even with high levels of particulates, while the fuel metering system is not, filter after protects the system from the actual pump introducing debris. Positive displacement electric pumps, fuel flows through the armature of the motor itself!!
 
I wonder if some put the filter after the pump to protect against the pump itself generating muck (e.g. the diaphragm shedding rubber). By the same token, you'd put the filter nearest the carb to catch any spall from the inside of the fuel lines.
 
ive had 2 for a few years now ,both get dirty ,so the one on top of tank dosent get it all,the filter just before the carb dosent need changing as often ,but still gets dirty
 
Thanks All - very helpful responses as ever. Will pop one on top of fuel tank (before pump). Particles have then got to defeat the gauze on the uplift pipe, the inline filter and the mesh in the sediment bowl of the mechanical pump to get near my new Weber carb! Tom
 
My universal filter is close to the carby.
I changed the glass one, after concerns on some LR forums, of it breaking, and it not being fine enough, to a universal plastic one, with an yellow paper? filter.
I realize this one could also split, putting fuel over the manifold, but haven't heard of them doing it. Did clean up inlet and outlet of it, with a drill bit as it was restricted by plastic internal moldings
My fuel tank was sand blasted and repaired. I spent half a day tapping it, vacuuming and blowing air through it.
The brass gauze is fitted to the fuel pump. Cleaned the bowl today. Its doing its job, but where did all the dirt/sand ? come from ? the inline pulls out finer bits. will have to pull the top of the carby and check the float bowl.

whitehillbilly
 

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I wonder why?
I think Mikeau hit the nail on the head on an earlier post. If the pump is after the filter and the filter gets choked, the pump only has the benefit of atmospheric pressure to push fuel through. Could easily end with fuel Starvation. If the filter is choked but is after the pump the pump will be more likely to push fuel through as presumably the pump will have an output greater than 0 barg.
 
where did all the dirt/sand ? come from ?
:) It's a thing I've wondered myself....what is that stuff and where does it come from ? I suspect a lot of it is rust particulates. At the bottom of an old float bowl it's very often red in colour and surprisingly gritty considering how many filters it goes through to get there.

When I was running a standard mechanical fuel pump onto a Weber I found that an additional filter after the pump, and with the extra pipework required to make sure the fuel line goes nowhere near the manifold, it was all too much for the mechanical pump to cope with. I ended up with fuel starvation at higher speeds.
So I then used an electric pump that had a built in filter before the pump. It pushed out enough fuel through the filter to cure the starvation problem.
 
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