ok so looks like I may have got this wrong. Again. We have leakage from the accelerator pump jet, which can have various causes which I have ruled out

What this does as well as fuel leakage is make mixture screw adjustments ineffective, nothing happens and that's not right, which is what made me look down the barrels to see the pump jet leakage.

Excess fuel pressure - no it's 2.5
Pump rod nuts too high - no, in fact at the bottom of their length.
Blocked or dirt in system - nah, cleared anything with compressed air AND previously it worked fine
Faulty diaphragm - nah, it's new and as above worked ok before
Faulty pump jets - nah, worked fine before
Vacuum leaks - Ouch, this is possible, but for later if the carb has to come off.

The last ting I did before refitting this carb was the float height, so that's suspect.

I will check it and make it err on the side of allowing less rather than more fuel into the float chamber. 

There are other possibilities like missing ball bearings and springs, but that's last resort as I am pretty sure they are present and ok.

There is also the fact this inlet manifold while gasketed with new Cometic gasket is NOT sealed with gasket paste, whereas the other one is, but I don't think it's that.

LATER: So this is driving be bonkers. However, I found the front carb pump accelerator arm was not moving at all; perversely since we have leakage. May be it's stuck in the open position. Might have to remove the carb to examine it as all components are underneath with access blocked by the dizzy. Certainly pump operation is counter intuitive. What looks like activating it is the opposite and what looks like not activating it is doing so.I have also adjusted and then un-adjusted the float height, but that made no difference.

Is this on both or only one carb Anthony?  Are the needle valves new, did you check their function before fitting float chamber cover?

23 minutes ago, anthonym said:

I will check it and make it err on the side of allowing less rather than more fuel into the float chamber. 

You don't want to be too far away from what it is meant to be as this will upset the fuelling, I would just see that it is correct.  Both need to be the same

Yes quite. However needed to rule it out. Duly adjusted for less, made no difference to leakage. Returned to 15mm. 

edit: so that means it is the same as the other one and both have the same droop, 25mm iirc . 

I'm hoping its something simple with the pump mechanism.

1 hour ago, OldAndrewE said:

Is this on both or only one carb Anthony?  Are the needle valves new, did you check their function before fitting float chamber cover?

Both carbs were refurbed during the rebuild, whether that involved replacing the needle valves I do not know. I have had the floats out and measured the fuel so often I am confident the needle valves are working. Getting the droop and drop right have been challenging, but I think they are ok now. It's the 15mm measurement that's so hard. Exactly where to measure it. Fuel pressure was way too high, but I fixed that ages ago. Filters are clean. I am thinking I may have to take it apart yet again to check if all the parts I think are there, are indeed there. For example there is a tiny ball bearing and such things always have a mind of their own.

Looks like carb off yet again to check function, esp the ball bearing check valve and etc

I just re found this, so looks like back to basics and start with this since it refers directly to dribbling and I have no idea how mine is set, the odds are its not correct being basically random. Now I know it is in fact impossible to check the pictured half millimetre, so I have to figure out some method to achieve the same idea, which appears to be no pressure on the diaphragm when disengaged.

I have just spent an hour (out walking) struggling with this mechanism in my head. I know it works like a switch; so it's not like a squeezy bottle where the more you squeeze the more and stronger the flow gets. One push at the "button" end (left in the above image) sets off the complete squirt (pump) mechanism. The things that can influence this are:

the accelerator pump JET size

the accelerator pump diaphragm SPRING (I have put "STRONG" ones in to get max squirt. ("Weak" is for better mpg)

the state of the diaphragm (old and feeble or new and flexible) 

and there is a ball bearing that prevents reverse flow and a weight somewhere - to check this I have to dismantle it.

Now then. A "not slow pump" of the accelerator pushes down the right hand end of the arm which pushes the button at the other end and releases the squirt of fuel.

A slow pump/press of the accelerator does nothing (not worked out how yet, just realised that's clever.)

My arm does not move at all when the other carb's arm does, so it's jammed. And in this pic  it looks like the arm is below horizontal with the lever casing, meaning the other end must be raised towards, if not pushing, the "button". So a horizontal edge along the horizontal of the casing might be a test to show if the arm is as designed; by which I mean from the image above, the right hand end of the arm should be higher than the left and generally the arm is raised at the right end and lowered at the left (where we can't see it). If I dismantle it I can look see maybe what degree is "on" or "off" the button. However, before that I can now explore the arm angle (having already removed the lock nut so it's only a twiddle with my fingers to adjust the height). Perhaps I can borrow some measurements from the other working carb's pump.

All the above is a bit convoluted so I have managed to make a comparison of the working and non working pump arms thus, granted the angles of view are different but it looks to me like one is drooping down (not working) and the other is angled up (which is working). When I say "not working" I think it still squirts fuel, but is also being held with pressure on the "Switch" button (which we cannot see) and so (I hope) is the cause of the dribbling fuel. I have since moved the HT lead.

and so that leads to the adjuster nut and right now I have only a pic of the working one thus:

Have to say they don't look much different regardless of one missing the lock nut.

And whenever I turn the key to ignition, before start, I hear a squeedgy noise from the front carb.. is the float valve faulty? I think maybe viewing the pump jets while turning on the pump to see if fuel leaks.. this only happens when the car has been resting a while... when I lift the float chamber lid (cover) the level always seem about right at 27mm i i r c. Certainly not flooded to the brim - maybe it's back to this pump action being faulty, if it's emptying by leaking I suppose it will replenish itself when the pump starts, when it should already be full ready for action given there is a non return valve one end and the .. whatever at the other end, it's a sealed system until its's not.

Hello, this doesn't look right, from two pics above, looks like a screw not done up properly.... Later: ok it needs nipping up, but it's not the faulty carb it's the "good" one. 

LATER: now then, now then, I removed the float chamber covers and fuel lines and blew through the fuel entry ports, while lifting the floats (one per chamber) until my air blowing was blocked. The rear carb was fine, the front carb was allowing air (fuel) until the float was much too high (despite my just having set it to 15mm) ; so I fixed that (bent it) and it now stops air (fuel) flow at what looks like 15mm (a.k. the float parallel with the roof.). Nope, no stop dribbling. However, it is nice to know these bits are working. 

So. Idea. With engine running, manually hold the pump arm higher than being held by the adjusting nut. E v e n t u a l l y the dribbling stops as I wind it up higher and higher. It feels like it's far too high, but the dribbling does stop. I suppose this at least identifies what/where the fault lies. I am wondering if I recall the new adjusting rod spring being significantly longer than the old one. Relevant? Not sure. Anyway, I have come away not least to have a cuppa to remove the taste of petrol and to allow the whole system to dry out a bit after I basically squirted fuel everywhere (lines off etc). 

I suppose what I have to do is keep winding up the adjuster nut (lock nut is removed) until the dribbling stops. I keep thinking that might stop the pump working, imagining the mechanism is doing my head in again. However, I think it won't.  Access is of course dreadful, fractional turns on the nut, dizzy cap has to be removed. Do NOT start engine with (hidden) dizzy cap off (again)!!

and Des Hammill says never shoud be more than 8mm of thread showing, looks like we still have room for that, given his 8mm includes the lock nut being in place.

ok so this is odd. 

Having removed the carb, disconnected the rod from the arm and removed the arm mechanism from the carb, , and manipulating the arm manually with the internal post on which it pushes, for there to be any gap, first I push the post outwards from inside the chamber and at this point there is .7mm of the arm protruding from the casing, so at this point the internal rod on which the arm pushes is touching but not receiving any pressure from the arm tip. So for there to be the .5mm gap specified in the image above (two or three posts above) the adjusting rod end has to have the adjusting nut screwed up beyond the 8mm limit, beyond which there is no thread on the rod. To push that far one would have to add spacers (a small pile of washers probably).

None of this is very encouraging as regards stopping dribble.

However, I have also dismantled the rest of the mechanism and blasted it all with compressed air, particularly the ball bearing non return valve. It's a ball bearing captive inside a screw, so I gave that loads of compressed air several times in all directions. I also blew through it to check with the ball bearing in different places the air can go through easily. So it's not and was not jammed, I did wonder if it was not rolling quite as it should, but it's difficult to get one's lips around it correctly.

I also found the long spring on the adjusting rod was on the wrong way around (mea culpa): delete all this, I made this mistake two minutes ago and then noticed and fixed it. 

I have made videos of all of this, but they are a bit long as I wander through this journey. 

Time to refit the carb. Again.

Here are the pics to go with the above:

Yes the locknut is not yet in place. The black tape is to save me repeatedly installing the Manometer take offs. 

The accelerator pump housing viewed from underneath upwards

Sideways view

Inside of the pump diaphragm chamber, showing the end of the actuator arm that pushes on the diaphragm "pole".

The diaphragm "pole" - and the spring under.

The diaphragm chamber

Where have you got to Anthony, have you refitted the carb yet?

yes just finished this second

I THINK MAYBE POSSIBLY I have solved the dribble problem, only to find that I now need the choke back in service. 🙂

The image above (several posts now) is/was reportedly from THE Dellorto workshop manual, which no one seems ever to have found a proper copy. So what is odd is (a) that it is impossible to measure the gap it indicates, because that gap is surrounded by solid metal. and (b) now I found a way to measure what I think is the same "gap", I find it is not possible to adjust the actuating arm so as to have the required gap. 

However, setting it to max on the adjuster we now have no dribble, at least not like we had before, it now matches the other carb and tends to be in response to the accelerator movements (not saying "pumps"). Pumps have always worked. There is no dribble problem on the other carb so if this one is now the same that's ok. Maybe we have a dribble problem when the accelerator is part depressed, but that will be for another day.

The real test will be whether adjusting the mixture screws now makes a difference whereas before they did nothing because the dribble was overloading fuel.

I just realised, there's no time stamp of our edits..

Meanwhile, one of the studs came out with the (crossthreaded?) nut. Refitted with loctite 243 (? no heat required) and replaced all 4 nuts with new ones. As ever spotted that the old threadlock on the stud was passed its best. However, not doing that today. I think all the studs need replacing, they don't looks as straight as they might be. I am noticing it is a vast number of small, inexpensive parts that on a car of such an age really need to be replaced; rubber has gone hard, metal (springs) all have fatigue, loctite (or whatever it was) has gone powdery. All that's needed is supplies and lots of time - and I guess not cost effective to get a professional to do it, bearing in mind my car (not the engine) has just been refurbished right down to Arch redoing the chassis. My instructions were to not touch the engine, but I failed to draw a line where the engine begins, so I have in this last year replaced all the ancillary things like cooling system (now works), 5 port Titan oil pump, sump (yes that IS engine), ignition system down to but excluding the mechanical advance springs and a million tiny bits inside the carbs.

Note to self: re fit the adjuster lock nut.

OK, too late for my suggestion

do tell!

it may well be coming off again - must be over 20 times now.

Sorry, got side tracked by dinner at my sister's. What I was going to suggest that before fitting, with the float chamber lid off, fill the chamber to the right level and observe. 

OBSERVE whether it leaks? 

I can do that without carb off - will try that next 

ahh except dribbles do not occur unless the engine is running, 

anyway I THINK we have dramatic improvement or even it fixed, just hard to believe my eyes. We will see when I get the manometer on it and try to set the mixture - I have to take the car away from the building for that as we have a new neighbour from a dark place.

4 minutes ago, anthonym said:

ahh except dribbles do not occur unless the engine is running, 

To me that implies that it is something wrong with the float/needle valve that is allowing the fuel level to get too high.

Does the engine have to be running or does it dribble with just the ignition on, i.e. fuel pump running

Yes I suspected that (not least you have mentioned your suspicion), but when I tested the needle valve and (again) corrected the float, it persuaded me that when the float reaches its max, the needle valve closes - as determined by me not being able to blow any air (my breath blown as hard as I might) through it, so if air cannot get through, neither can fuel. It made no difference to the dribbling. 

Engine has to be running. Fuel pump alone, no engine, no dribble.

To save you reading it all, the above several posts find that the accelerator pump actuating arm adjusting nut has not been high enough up its adjustment thread. This leaves the accelerator pump diaphragm under pressure whereas the diagram several posts above requires there to be no pressure at all, as defined by a 0.5mm gap. 

I have now maxxed out the adjuster and I THINK the dribbling has stopped. I noticed under acceleration (not pumping) both carbs were dribbling, but that is for another day if ever depending on what I find next during the mixture tuning process. Up to now the front carb has not responded to mixture changes presumably because it was being flooded by the dribbles.  No dribbles also seems to mean I need to reactivate the choke.

Struggling to think of a reason why engine running (presumably at a constant speed) should make a difference.  Anyway hopefully you have found a solution

yes tick-over - and yes me too. Later: had a thought, when running just the pump no engine it is just that, to start the engine I have to activate the pump jets to start it.. so there is that difference; I will try running the pumps no engine AND pumping the jets a couple of times.

if it is a solution it might be a bit frustrating not knowing why - though if it is "the adjuster was not adjusted high enough" whereas the other carb was/is already I suppose then I will be thinking I should have spotted that on day 1 - in my defence when mounted it is practically impossible on this carb to see the adjuster and where it is on the scale.

The way the pump works does my head in, it's all counter intuitive.. activated by the right foot, but operated by the arrangement of springs and the jet (choice).

Morning update: where I am at is having had so many attempts at different solutions to stop the accelerator pump jet dribble I am having trouble believing it might be fixed, and so simply; although I suppose dismounting and dismantling and remantling a carburettor may not be seen as simple, but in the end it amounted to tighten a nut further up its available thread.

However, on a quick start up this morning it was much more difficult to start, I expect because we no longer have the dribble fuelling start up and while several pumps can persuade it to start, I suspect reattaching the choke would be better. Granted when we are able (finally) to go through the mixture tuning process the choke may no longer be required.

So having had to use the accelerator pump to get the engine started and then viewing inside the two barrels of carb no 1 (the front carb), while there were what looked like "remnant dribbles" after a pump, these SEEMED to reduce to nothing where previously there had been much larger droplets constantly dribbling from the jets in each barrel.

I have always run the choke connected on my Dellortos and used it for cold starts.  Unlike Webers it seems reliable