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.