Fuel leak from chamber below enrichment device

[Mrmci]

Hi chaps,

I really need some help. My Elan sprint has a fuel leak from the chamber shown in the attached photo, I've managed to get the cover off in situ.

My Weber 40 type 31 carbs have been ultrasonically cleaned and rebuilt with new gaskets etc, to help to fix a fuel leak but it's not fixed the problem.

I've had the carbs filled with fuel and sat on the bench and no signs of leaks but on the car, after running, this chamber has about 3mm of fuel at the bottom, which is them seeping out while the car is stood.

The solder bung has been epoxied over just in case this is the leak but it is still leaking. I think it's happening on front and rear carbs.

Any ideas really appreciated.

Cheers

Mark

[alanr]

The throttle spindles pass through that chamber so I would suggest the fuel is more than likely leaking along worn spindles and bearings This to me is the most likely suspect..
Alternatively, but I suggest more unlikely, fuel could be leaking into the chamber via the cold start device situated above it. You can buy from Eurocarb a blanking plate to completely eliminate the cold start device if this does turn out to be the problem.

Alan

[Mrmci]

Thanks v much for the reply Alan. The throttle spindles and bearings were checked at the rebuild and appear to be good.

I'm starting to think the fuel must be coming in from above so perhaps it is worth trying the blanking plate idea, I don't use the fuel enrichment device.

What I don't understand is there is a gasket up there so don't see how that much fuel can "slosh" in

[alanr]

Also does the chamber back plate have a hole in it? There is a theory in some quarters that it is possible to get a vacuum in that chamber which sucks fuel into the chamber via the spindles.The newer Webers have this hole fitted as standard.
Usually when Webers are now rebuilt by the likes of Eurocarb etc they fit the later type chamber back plate which has a 10mm hole in the centre. Alternatively you could drill your own hole in the chamber plate.

I have '31's on my car and I have the chamber plates fitted with the large centre hole. May be coincidence but I have no fuel leaks from my Webers at all anytime.

Alan.

[Mrmci]

Ok, that makes sense. I know that the 151s have this hole and the gasket actually has a hole in this location. I may do a test run with the plate off and see if it makes a difference.

Good call! Thanks

[Craven]

Absolute classic worn out carb’s, hole in plate will help but their passed their sell by date.

[elanner]

There are lots of threads in the forum about this.

This worked for me:
- Drill a vent hole in the accelerator pump chamber cover.
- Lower the fuel level in the float chamber a smidgen.
- Use the starter circuit every time to keep it clean and stop it from gumming up and potentially sticking open (or close it off completely with one of the after-market kits).

Nick

[Mrmci]

Thanks Nick,

I had a search of the threads but I think I struggled as I didn't really understand what that cover plate was till I took it off.

I'm going to try your suggestions.

What I don't understand is how the fuel gets in there. All of the apertures at the top should be lower than the fuel level in the bowl and there is a gasket up there anyway.

Cheers

Mark

[512BB]

'Absolute classic worn out carb’s, hole in plate will help but their passed their sell by date'

If the float levels and everything else is equal, I agree with the above statement. I had the exact same problem that the op describes 40 years ago! Tried everything including rebuilding the carbs and upgrading the cover plate to ones with a hole, but after a short while, the drip drip drip came back when the engine was stopped.

I solved it in the end.

Leslie

[elanner]

What I don't understand is how the fuel gets in there. All of the apertures at the top should be lower than the fuel level in the bowl and there is a gasket up there anyway.

I never figured it out either. As Craven mentioned, it's surely wear somewhere in the carbs!

Fortunately mine are hanging in there and are currently fine. No drips and pretty much always nice and dry underneath. Very occasionally there's a small damp smear under the flexible mount, but that's it. I keep an eye on them!

Nick

[Mrmci]

Ok, understood. Thanks all.

Is there no way to refurbish the carbs to retain originality?

If not what are the best replacement carbs? Spanish 151s? Can these be jetted with the same as the original 31s or would it need to be rolling roaded?

[2cams70]

Unless anyone can actually identify scientifically the source of the leak I for one refuse the accept that it’s just “general wear”!! Virtually everything in the carb is replaceable after all.

[Craven]

2cams70
You have stated your position before but if you accept there is a vast amount evidence that leaks from this area on old 40’s is almost common place and many attempts by many people over many years have not identify the reason then it must surely be multi factor or accumulative effect not a single scientifically identifiable source, in general terms just worn out.