320/6 fuel system

[AndyBaur]

I know this sounds like an odd question but can anyone tell me the correct route of the fuel line to the carb/fuel pump for a Weber fed 320/6.

The reason I ask is because when I fitted new fuel hard lines I thought I would complete the job by changing all the rubber fuel lines in the engine bay even though they didn't look terribly old. I just changed the lines one by one cutting the new hose to the same length as the old one & installing it in its place.

I hadn't really driven the car before this work so I can't say if it had this fault previously but if the car isn't started every few days then it struggle to fire. Leave it a couple of weeks & the system has to be 'primed' by disconnecting a fuel line & putting petrol directly into the carb & pump.

I thought this airlock might be down to porous gaskets so pulled the fuel pump out for a clean up & new gasket. Once it was clean I noticed a small arrow cast into the pump which suggested the fuel came out of the lower pump body with the fuel going into the top of the pump.

Now, should the fuel from the tank go directly into the top of the pump, out of the lower pump port & into the top port of the carb with the lower carb port returning fuel back through the charcoal canister to the fuel tanks?

On my car, the fuel comes from the tanks through an after-market in-line filter into the top port of the carb, out the lower carb port, through the charcoal filter into the top of the pump and finally out of the lower pump port back to the tank.

This doesn't seem right to me as the pump is having to suck through the charcoal canister, carb & in-line filter before it can pull fuel through.

The Haynes manual is, as expected, totally useless here.

[BertjeConti]

First: fuel does not go through the charcoal cannister!

The function of the charcoal canister is to catch fuel fumes from the fueltank.

The fuelpump suckes fuel though the fuel deliver line from the tank and pumps it into a low pressure regulator located at the original 4a1 carb.
From the regulator the exessive fuel runs back to the tank through the return line
Another line from the regulator feeds the low pressure regulated fuel to the carburettor.

[AndyBaur]

Ok, so it's not a charcoal canister. You can blow through it easily but you can't see through it so the line must be taking a circuitous path through whatever-it-is - I'm now guessing it must be some sort of expansion chamber. It doesn't have any arrows on it so it mustn't be directional.



My car has a Weber (I wish I knew which model) instead of the Solex which is why the manual is of no help.

I want to confirm that the fuel line from the tank goes into the TOP of the pump & out the lower port to the carb. There is no regulator with this set up - do I need one?

I guess the 'expansion chamber' must go between the pump & the carb (I can't see any point in having it in the return line from the carb).

Maybe all this explains why there is such a flat spot at low revs - the engine isn't getting enough fuel when the throttle is opened.

[nas80]

i have never seen an expansion chamber on a carb or indeed any fuel system?

Are you sure that's not a fuel filter?

[Desmos]

Just had look at mine:
Front exit from pump goes to the lower carb pipe.
The upper pipe from carb is return to tank.

[AndyBaur]

Front exit from pump goes to the lower carb pipe.
The upper pipe from carb is return to tank.

Well I've got the carb connections the wrong way round then. I'll swap my connections over. By 'front exit' you mean the lower pump port? I have:

Tank ~> 'Expansion/Filter' ~> top pump ~> bottom pump ~> in-line filter ~> top carb ~> bottom carb ~> tank.

I have it started & running (idling) but when I try to drive it more than 1/4 mile it starts to hesitate. If you watch the clear filter you can see air bubbles coming into it every now & then so it's sucking air in somewhere. I'm not sure the expansion/filter is actually doing anything so I could remove that & run the feed from the tank directly into the pump.

[Desmos]

From the fuel pipes from tank:
Front pipe to pump in (top connection of pump)
Lower pump connection (with little out arrow) to lower carb connection
Top carb connection to rear pipe (returning to tank)

[AndyBaur]

Success! Thanks Desmos, your advice worked a treat. The low speed flat spot has now gone & 80mph can be held on just a whiff of throttle.

I don't know who did the Weber conversion but they had the carb inlet & outlets mixed up & the 'filter/expansion' thing in the carb return line to tank. I'm not sure how it was running at all.

Let's hope it starts easily after a week of standing.

to the BMWE21.net forum!

[Desmos]

High 5's all round

[mcjjordan]

That looks like a fuel cat
Inline system that adds lead to the fuel system so can run on unleaded