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Discussion Starter #1
Hi all,
continual fuel starvation issues causing the carby to run dry explains why im here with the fuel tank out, as I have diagnosed the problem to gunk in the fuel tank.

The fuel supply/pick up point in an Alfasud fuel tank is from a baffled area in the middle of the tank that also houses the sender unit.
This area has been running dry whilst there is still fuel in the rest of the tank.
there are larger gaps at the top of the baffle that allow fuel into this compartment when filling up, but these no longer function as the fuel level falls.
There should be some smaller holes or passage allowing fuel into this compartment of the fuel tank when the fuel level falls which must be clogged up.

Can anybody tell me where these passages should be so i can try to unplug them by poking around with a plastic probe?
Or an indication as to what size they should be so i can punch or drill new holes to allow fuel to flow into this compartment?

See pic 1 of inside the baffled compartment, one side of the partition houses the sender unit float, the other the pick up pipe.
as you can see its pretty rusty and full of stale lacquer in there, and that's after a bucket of foul smelling crud has been flushed out.
i have made a much larger fuel tank pick up mesh to cope with the condition of the tank in the future, see pic 2, that little thing that resembles a dried out prawn skin is the original fuel tank filter mesh.
i also plan on running a second paper filter before the fuel pump, and i guess more frequent fuel filter changes are part and parcel of owing a 40 year old car.
 

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Discussion Starter #2
ok so i managed to punch a hole near the bottom in the internal partition part of the fuel tank using a crowbar and hammer. I was working blind as the tank was flooded with water so i wouldn't blow myself up with a spark and unfortunately i overdid it, see pic 1. Now to reduce the hole size so that it doesn't run dry on a slope or a long right hand bend.

I settled on a 6mm hole, as anything smaller would gunk up again with rust flakes, anything bigger might drain dry too quickly on an incline or long bend.
i used a piece of fuel hose, see pic 2 and 3, as this arrangement should control flow in and out of the compartment better than just a hole in the side wall.

Anybody considering trying something like this should be aware the air fuel ratio when the tank is empty could be is very explosive.
 

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I used to have that problem on my 1981 Mercedes 300GD.
Someone told me to use Aderco 5000, is a dispersant, very concentrated( 1 ml. per 5 litres of fuel). This stuff is used in maritime tanks, where have a lot of problems as yours.
Since I am using it, I have never had a problem for years.
 

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Not saying that this is your problem as it looks pretty messy in there but I had a fuel starvation issue at high revs on a twin carb boxer years ago that I couldn't track down the cause. Turned out to be the fuel line fittings on the carbs. The two pipes are different diameters on the carb and there is most definitely a "In" and a "out" I had put the line from the tank onto the fitting on the carb that feeds to the "other" carb
 

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Discussion Starter #6
It is pretty messy in there, that's why im not keen on using any additives to dissolve it any further. My car sat unused for 5 years and developed that foul stale fuel smell. Additives may be good to maintain a tank so this doesn't happen, but this one needed a flush.

I have decided to put 2 of the Alfasud cheap plastic disposable type fuel filters after the pump, that way if the first one clogs up, i can quickly remove it and get the car going again before the traffic banks up too far. I am still traumatised by that feeling of the throttle going dead from fuel starvation on the overpass during peak hour traffic.

Alfasud mechanical fuel pumps need to be looked after as they are no longer available, but i think the pump should be able to pass small debris without any problems.
So i put a 3rd metal mesh filter before the pump, in the form of a modified Alfetta/105 style glass bowl type filter housing with a fine metal mesh instead of the paper element.
This mesh is much finer than the one on the pick up pipe in the tank so cleaning will be much easier in the engine bay as the tank wont need to be lowered.
See pic with ruler showing mesh in tank about 1mm and mesh before pump about 1/4mm, and pic showing metal mesh instead of paper element in the 105/alfetta filter housing.
The inlet fuel hose of the alfetta/105 filter is the same 5/16 diameter as the alfasud supply hose.

Last 2 pics show my new filtration system, 2 disposable filters after the pump and an alfetta/105 filter before the pump.

A new tank would be nice, as this is not the first Alfasud i have had that suffered from fuel starvation. So far i drove the car all day today with no problems, although with a full tank of fresh fuel.
 

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The fuel filters did nothing to prevent the very fine rust getting to the carb. One look inside the tank was enough. The rusting tanks, I have two Suds, were a mess and replacing the tanks was the best option over the kit to refinish them internally.
 
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