40 DCOE Webers flooding

[4129R]

I have just got 3089R running after many years and there is a problem with fuel dripping out of the inlet trumpets of both 40DCOE Webers at high revs.

I have checked float levels, I have thoroughly cleaned out the little barrel filter as the fuel enters just after the banjo, I have cleaned out the needle valves which the floats push on, the floats are not damaged, but when the pump is pumping at high revs (over say 3000), both carbs are dripping fuel.

Why is this happening to both Webers? Is the fuel pressure too high from a standard AC Delco mechanical pump?

Luckily I noticed this before venturing out on the road.

Googling 40DCOEs flooding, it seems this is quite common. 3.5psi seems to be the correct fuel pressure. I wonder what pressure my AC Delco is pushing out. 

[jbcollier]

You can get inexpensive vacuum/pressure gauges from most automotive parts suppliers.

[EuropaTC]

Hi Alex,

I have a vague memory of the modern mechanical pumps pushing more than the old glass bowl ones but I can't remember where I saw it at the moment. 

When I fitted an electric pump to the Elan I also fitted a regulator even though the pump was supposed to be low pressure for carb engines.  That was because Des Hamill quotes 1.5 to 2.5 psi in his book and says both weber & dellorto need high volume but low pressure. Hence I didn't want to chance the supposedly 4psi of the pump overrunning the float valves.  It's set at 2psi but whether it is 1, 2 or 3 I honestly have no idea, it's just what it says on the body.     You shouldn't need one with a mechanical pump but if you had a regulator kicking about I think I'd drop that in the feed line and see if it makes any difference.

I see you've cleaned everything, confirmed float levels and that they do float.  I suppose the next step is to try replacing the needles/seats with a service kit just in case they aren't sealing even if they are free to move.

High pressure fuel delivery would apply to both webers, less likely that both webers have identical needle valve seat problems but it's something to bear in mind because something is allowing the pump to override the normal cut off and cause the flooding

Brian

[4129R]

I suppose the next step is to try replacing the needles/seats with a service kit just in case they aren't sealing even if they are free to move.

They are about £8 each from QED.

I will phone them on Tuesday. (Monday is a public holiday here).

[jbcollier]

If the pressure is too high, rather than flowing in, the fuel “squirts” in disturbing the fuel already there, making it turbulent and wash up higher causing the flooding when the floats are set correctly.  Usually the stock pumps do not have high pressure output but it is the first thing to check.

[4129R]

Well there are 4 different sizes of float valves foe DCOE Webers, 150, 175, 200, and 300, so presumably, like the main jets, that equates to 1.5mm, 1.75mm etc.

QED tell me that a 1558 TC pushing out only 125bhp requires a 175 needle valve.

They told me that a standard mechanical fuel pump has been known to pump at too high pressure (3.5psi seems to be the limit) , so if new float chamber valves don't cure the flooding, my next thing to do would be to fit a fuel pressure limiter on the output from the fuel pump set to 3.5psi.

[BERNIEHUMBER]

HI:
I had the same problem with a 45 on my Hermes conversion.
Put in a pressure regulator set for 2 psig ..end of problem.
It was very disconcerting that smell of gas heading down the 401.

[4129R]

New 175 float valves fitted. Petrol still dripping out of Webers. Manually adjustable fuel valve on order. I wonder why this one decided to leak fuel, and the others didn't. This one has a new AC Delco pump, which must be pushing out more pressure than the others. Maybe I need to take a much closer look at the others to make sure they are not flooding either. 

[4129R]

Fuel valve limiter arrived. I fitted it the wrong way around, and it leaked badly.

Now fitted the correct way, and after an initial problem, I turned the pressure down to 2.5psi, and it seems to have stopped all the flooding.

I will check regularly to make sure it is not dripping. I think carrying a fire extinguisher which is easily accessed is a must on old cars, where just a small leak could be terminal.

[Dilkris]

Please keep us posted with this - I have a similar problem, but it appears (in my case) that the accelerator pumps when activated are simply pumping too much fuel into the carbs; this of course can be adjusted if this is actually the problem but is it? Could be high fuel pressure, poor float valves or ..... I don't know yet.   
I am on a learning curve and "information seeking" venture with the issue.   

[4129R]

The fuel pressure valve is working well.

https://www.ebay.co.uk/itm/386223935265

[BDA]

I don't have nearly the experience JB has but I've read about dozens of disasters on the interweb that were caused by fuel pressure regulators. It's been a while so I don't remember what brand regulator they had or if they mentioned. Several of the people who had problems swore off them completely. The impression I got was that they were potentially dangerous enough not to bother with any of them.

Keith Franck is my Weber god. I would have him tune mine but he's on the opposite side of the country (US) from me. As an indication of his knowledge and expertise, he makes his own series of emulsion tubes, idle jets, and accessories. He can be contacted at his sidedraft groups.io site (https://vintagetechnologygarage.groups.io/g/sidedraft). All that is to say that I am just a messenger here and I have reason to value his opinion.

He recently posted an interesting post about electric fuel pumps and fuel pressure:

FYI, DBE has been selling the 7psi mechanical fuel pump for about 15 years now. I bought one about that long ago and it works a treat without a fuel pressure regulator. Ignore all the experts and the Weber Tuning Manual because they all are wrong. I don't want you chasing a false lead because it will not solve your problem.

Years ago I brought Ken at DBE up to speed on this situation and advised him not to freak out.

Just do the math of the leverage of the float. The ratio is about 4:1 from the lever arm of the pivot to the valve versus the buoyancy of the float to the pivot. The float has plenty of extra buoyancy to handle that extra fuel pressure.

What is in jeopardy is the lobe on the jackshaft. The 7psi loads the jackshaft to the point it wears out quicker. I've already had to replace the jackshaft once on my Elan.

Just to make my point I installed a 5psi electric fuel pump on my Lotus41 which has a pair of 45 DCOE-152 carburetors.

For the record, I use a Facet cube fuel pump. It's been a while since I checked the pressure it delivers but I think it's something like 3 or 4 psi.

With respect to your fuel dripping issue, he recently had a couple of posts that may have bearing on your issues:

On sidedrafts when the fuel is flowing through the main circuits it is also leaking fuel from around the outside of the air horns. To prevent this you need to use this extremely viscous and sticky polyester sealant to stop that leaking. Do not try to use anything else or whatever it is it will eventually end up clogging up the jets. This stuff stays where you put it period.

Besides the air horns, he recommends using it on idle mixture screws to ensure that they are not the source of an air leak. For the record, I do have it on my idle mixture screws but I have not tried it on my air horns though I will be doing that soon. You can get EZ Turn at Aircraft Spruce (https://www.aircraftspruce.com/catalog/cspages/ezturnlube.php?clickkey=5414).
Here is the second post concerning fuel dribbling:

If you believe one cylinder is being fed more fuel then the first thing you need to do is peer down the throat and look to see the AV or the accelerator pump nozzle is dribbling in fuel due to siphoning. You need to rev the engine to high rpms up so the main circuit kicks in before you take a look otherwise the siphoning may not get started in the AV.