Weber 32/36 DGV Issue

[Puddles of Oil]

I have a Weber 32/36 DGV twin choke eon a Rootes 1725 engine. It is brilliant, fast, smooth and economical. It has been in place for a long time and I know the jetting is correct.

On very hot days I sometimes suffer from fuel vaporisation and can see the petrol bubbling in the glass fuel pump bowl. When it cools down again the car restarts.
To prevent this I added a low pressure electric pump into the fuel line. The idea was that when the petrol is vaporising in the mechanical pump I could turn the electric pump on and re-prime the mechanical pump and carb. 99% of the time the electric pump would be turned off.

Since doing this a couple of days ago I have had problems with the carb running very rich. If I take the plugs out they are dry but sooty black and the car is running poorly.

I have followed the set up instructions to the letter with regards to the idle speed and idle mixture screws but the idle mixture screw has little effect. I can screw it all the way in and the engine keeps on running, if I back it out more than about 2 turns it will start to stall. I have taken the carb to pieces and blown all of the passages clear with a low pressure air line, I can't see anything blocked or wrong. Even with just the mechanical pump priming the carb from being completely dry it still just runs very rich.

Is there anything that I could have damaged in the carb by possibly over pressurising the fuel? Is there something else I should be looking at? I was due to do a 500 mile trip this weekend, doesn't look like that will be happening now.

[Huntsman]

Is the level of fuel in the float bowl still correct?

Are you sure you havent created an ignition or timing fault while tinkering?

[TonyRPH]

Does it have a fuel return pipe to the tank?

If not, I suspect the electric pump is overwhelming the needle and seat with pressure.

These carbs were not designed with high fuel pressure in mind, and in fact the later Fords fitted with any model of Weber typically had a return pipe to the tank (I believe this was also an emissions 'thing' to prevent rich running).

[Puddles of Oil]

I checked the pump pressures tonight. The mechanical pump supplies fuel at 2.5psi, the new electric pump pumps at 4psi. Still low but higher than a Weber likes.
I am starting to think that a bit of dirt might be blocking something in the idle circuit. That would give the symptoms I've got. I am going to give up on the electric pump idea and remove it, I just want to get it back to how it was now!

[Puddles of Oil]

I think the fuel level is unchanged but will check it, it doesn't have a return pipe.

I don't think I have created an ignition or electric fault. Initially I thought it might possibly be a distributor/timing issue so I swapped one over but the problem was the same.

[Anoymously101]

I had an Alfa with a 36DCD weber which had fuel vapourisation issues when it was in traffic - I live in London, so that's a pretty common occurence. It alreday had a facet electirc pump and a filter king to control the pressure. I fitted a phenolic (?) spacer between manifold and carb. This cured the issue effectively. Bought from a company on e-bay called Fast Road Cars. I'm pretty sure the spacer was meant for a DGV carb, but fitted the DCD. If you don't have a spacer already maybe try that a simple fix to the fuel vapourisation. Not sure what has caused the new issues though however - maybe fit a new needle valve in the float chamber.

Jon

Edited by Anoymously101 on Friday 5th July 08:00

[TonyRPH]

Puddles of Oil said:

I think the fuel level is unchanged but will check it, it doesn't have a return pipe.

I don't think I have created an ignition or electric fault. Initially I thought it might possibly be a distributor/timing issue so I swapped one over but the problem was the same.

Everything points to an excessively high float level (with your current rich running issue) - or as below...

I would check the float level, not only by measurement, but ensure the float chamber isn't too full when you remove the top of the carb.

I'm assuming that when you stripped the carb, you haven't mixed up the primary and secondary main jets (and air corrector jets)?

The emulsion tubes are likely to be the same type - you can check this visually, but there's usually a number stamped on them, usually prefixed with the letter 'F'.

[Ambleton]

Here's a thought.
With modern fuel and over pressurising your carb, I wonder if your floats have a started to take on a little fuel and therefore don't have the buoyancy to fully shut the valve.

I don't have any experience of this carb, only the side draughts but 4PSI is a little high for a Webber in my experience. We used to set them at 3.5PSI.

I'd set it all up on the electric fuel pump only initially with the carb loose and put some blue roll under it. You will soon see if the carb can deal with 4PSI.

[Puddles of Oil]

Thank you for all your responses. I am still struggling on with it. I stripped it all down today and cleaned through everything with carb cleaner. The filter inside the carb had some crud in it which was a surprise as it is downstream of another fuel filter.
The float seems to be as I would expect and it appears to be closing correctly.
Whatever I do I just can't seem to get it to run on the idle circuit. I can literally turn the idle circuit mixture screw all the way in and it will still run. I have followed the instructions with regard to backing off the idle speed screw and I understand why this is done. There is a tiny adjuster screw in the base of the carb that is adjusted from below and raises the linkage. That never seems to be referred to in the tuning instructions. Could be an issue? If so how is it supposed to be adjusted?

[Puddles of Oil]

This is the screw from underneath that I am referring to.

[TonyRPH]

Puddles of Oil said:

This is the screw from underneath that I am referring to.

That screw is the limit stop for the second choke (barrel).

You shouldn't touch that at it's typically set at the factory. It sets a tiny clearance between the butterfly and the barrel, to ensure the second choke butterfly doesn't seize in the barrel.

The carb looks quite new, so the float should be in good condition - if you remove the float completely and shake it, is there any petrol inside it?

I used to test them in hot (not boiling) water and check for air bubbles, which was a sure sign the float had a leak.

EDIT: Is the secondary butterfly closing fully? That would cause rich running if not.

Edited by TonyRPH on Friday 5th July 11:21

[Puddles of Oil]

…… what do you do if you have touched it?

[TonyRPH]

Puddles of Oil said:

…… what do you do if you have touched it?

Get the thinnest feeler gauge you have, insert it between the butterfly and the choke tube and adjust the screw for minimal friction.

That should fix it. If at some future point you find that the second choke seems to be sticking you may need to allow a little more clearance.

After several thousand miles (depending on engine condition) it's quite normal to get a carbon build up around the secondary butterfly especially - this can also cause a sticky secondary.

[Big_Dog]

I take it the tank is vented properly?

[hidetheelephants]

Remove the electric fuel pump, place it on a shelf in your workshop and then buy some thermal wrap and put it around the fuel pipes between the pump and the carb.

[Legacywr]

I didn’t see it mentioned… do you have a pressure regulator fitted?

[Puddles of Oil]

Tank is venting. Electric pump has been removed (I wrapped the pipes with heat shield and re-routed them away from the heat long ago). There was no pressure regulator when I had the electric pump fitted).
I will set the height with a feeler gauge as described.
Thank you.

[Legacywr]

Without a regulator the fuel pressure can be more than the pressure being applied to the needle by the float.