Lotus Elan

Weber leaking

PostPost by: reb53 » Tue Jan 31, 2006 11:34 am

Out in the country having a drive in my Sprint the other day when the smell of petrol became really obvious.
Checking everything I found a wet area and a few drips coming out the bottom of the small plate between the chokes at the front of the carb and below the cold starting device. Is it reasonable to assume that the cold s. d. is at fault?How fuel would get into this little chamber any other way I don't know.
Reading old posts the suggestion is to blank it off and plug it up. Is this still the suggested cure? I can do without it as I've never needed or used it.
Float level is OK, everything is moving freely, choke lever not jammed on and I haven't been messing with anything.
It coincided with the idle becoming really rough but this seems to have corrected itself as the leak lessened. Still there, no longer actually dripping, but still smelling really bad.

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PostPost by: twincamman » Tue Jan 31, 2006 12:04 pm

Don't fool with gas ---it probably wouldn't be passed as a fuel source today-----the first place I would check is at the banjo fittings where the fuel enters the carb -check tightness but don't over torque the fitting bolts also check the fiber seal washer behind the fitting ---also there may be a small leak in the gas delivery line --:shock: ed
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PostPost by: reb53 » Wed Feb 01, 2006 5:09 am

All the fuel lines are OK. The leak is around or actually coming from the little plate between the chokes at the front of the carb and below the cold starting device, (which I always used to call the choke but I guess on carbs and especially Webers that can get confusing!)

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PostPost by: john.p.clegg » Wed Feb 01, 2006 6:53 am

Accelerator pump? Maybe needs a new diaphragm?
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PostPost by: reb53 » Wed Feb 01, 2006 8:21 am

The accelerator pump appears to be working as it should in that it lifts up easily and slowly drops without binding or getting stuck.
I remember replacing diaphragms in my S4 with Strombergs but Webers don't have any do they?
Mind you I am a bit suspicious of any rubber component coming into contact with fuel since switching a few months ago to new higher octane BP . Highest available around here at 98 but being lead free is full of all sorts of crap that plays hell with old rubber components. I didn't think I had any but now I'm not so sure.
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PostPost by: twincamman » Wed Feb 01, 2006 1:19 pm

being as you are in NZ the only thing I can think of then is that the fuel is being affected by reverse gravity and leaking out the top---- :shock: ed
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PostPost by: type26owner » Wed Feb 01, 2006 1:41 pm

Hi Ralph,
The cold start units do leak fuel internally and externally. The piston that gets lifted up by the cabled driven lever covers five holes when fully seated down or closed. If the piston is moved at all up it uncovers three of those holes immediately. One hole is the large ~5mm passageway to the downstream side of the butterfly. Another ~1mm hole meters in fuel and the third is an outside air bleed. Further up there is another set of fuel and airbleed holes.

The point is that if you just install a blanking plate the pistons will be loose enough to possibly get stuck unseated with only gravity and a wimpy spring holding them closed. This can cause an internal fuel leak if the pistons get stuck up. The fuel leak externally will br fixed though.

I have glued in plugs to seal off the pistons bores and installed the blanking plates. It sucks in cold weather to not have them working. However in about twenty seconds there is enough heat built up in the combustion chambers so the engine can vaporize the fuel well enough to idle at little slow but okay if the carbies state of tune is perfect.

The other fuel leak to fix is the paper gasket under top float bowl cover. The newer rubber gasket can be kludged into service and I've posted how to do that here some time ago. The fuel dribbles out around the air trumpets also. That can be stopped with a homemade gasket or sealant.

I already had a flash fire which charred but did not penetrate the fuel line that goes from the tank to the mechanical fuel pump. :evil:

The perfume of fuel will always be there to some extent without a charcoal vapor recovery system. Mine reeks when you get up close to the front grill.
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PostPost by: redelan64 » Thu Feb 02, 2006 8:55 am

Hi Ralph,

The problem you are experiencing is very common on these carbs and is particularly dangerous if not checked given the position of the distributor below.
I have written a paper which I can email to you on the solution to leaking webers.
Most of the problem was solved by drilling a hole in the cover plate.
I found this out after exhaustive tests and wrote to Weber only to have them say that this was an update in later models.
The problem is that when you are driving with throttle open and then shut it, a huge vacuum is created which simply draws air from any opening.
The clearance in the shaft to housing allows the vacuum to draw from the throttle chamber and thus pulls small amounts of fuel from the pump lever passage.

This fuel eventually seeps to the bottom and drips onto the dissy. One flash and your Lotus is ash.
I have also 'lapped in' the choke piston and this also reduced leakage under vacuum.
On racing engines we use weber lead shot and plug the fuel circuit gallery to the cold start circuits to make sure.

Hope this help - try the hole at 1/16" towards the top of the plate.

Regards

Craig
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PostPost by: type26owner » Thu Feb 02, 2006 2:23 pm

I completely forgot about that rear coverplate weeping fuel. Rather than introduce an airleak to break the vacuum I sealed the coverplate to make it liquid tight. Used some adhesive which is dissolved instantly by laquer thinner but not by gasoline otherwise the plate can't be removed without destroying it. Can't recall what that stuff was at the moment though. :?

Craig, I'd like a copy of your paper please. Thank you.
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PostPost by: Dave-M » Thu Feb 02, 2006 4:37 pm

Hi guys,
I must be missing something here, maybe someone can explain exactly where the fuel in the central chamber is coming from?
Assuming maximim vacuum on over-run, if the worn spindles are allowing vacuum to develop in the chamber air will be allowed through from the top of the float chamber via the 10mm hole housing the return spring and to a lesser extent down the side of the pump actuation rod. There is no where fuel can be introuduced into the chamber other than down these two places and to do that the fuel level in the float chamber would be so high as to prevent the engine running. Drilling a hole in the closing plate will have no effect other than to reduce the vacuum induced in the float chamber. So I conclude the fuel must be coming from elsewhere.
Probably from the choke link housing and running down the outer face of the central chamber closing plate.
What do you think?
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PostPost by: type26owner » Thu Feb 02, 2006 4:45 pm

Dave,
It does this when the lateral forces approach 1G. The fuel sloshes around then. Just putting around and it's not a problem.
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PostPost by: Dave-M » Thu Feb 02, 2006 7:42 pm

Kieth, G force cannot cause fuel to be spilled down the return spring hole or the accel pump actuating rod as they are sealed by the top cover and its gasket. If the top cover was loose or the gasket faulty it could happen.
Reading the original post I would suggest maybe the float/needle valve had stuck open for a short time causing fuel level to rise and the cold start valves to leak around their perimeter and run down the back of the carb.
A simple way to disable the cold start circuit and retain a standard appearance to the carbs is to simply soft solder the inlet holes at the bottom of each cold start jet. This is the only way for fuel to enter the circuit.
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PostPost by: type26owner » Thu Feb 02, 2006 8:04 pm

I did not say it made it's way down via the springs because I'm well aware that area is sealed off. Fuel does get on top of the accelerator pump piston and sloshes over onto the top to the actuating rod. IIRC, there is bleed hole above the pistons to prevent a hydraulic lockup, that's the culprit since there not a one-way check valve. Try it with the carburetor loose by gyrating it around and you'll see the fuel dribble down into the cavity if you leave off the coverplate.

Only soldering the cold start jets closed only cures half the leaks. The blanking covers to replace the cold start units have a zero chance of being air-tight since they flex out of shape when cinched up. You'll likely have a large airleak which will cause the AFR to lean out to the extreme and cause an annoying popping on overruns.

The paper gasket for the coverplate was a joke on my DCOE_18s. Both my castings had the same casting flaw were about 8mm of the sealing surface was missing so the gasket was useless. Of course the flaw was on the bottom edge so the fuel poured out as fast as it came into the cavity. No vent hole was going to stop it either. I'll bet almost everyone that has DCOE_18s has the same flaw.
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PostPost by: reb53 » Fri Feb 03, 2006 7:48 am

Having started this I'd better come back in here! Re " reverse gravity " causing the fuel to come out the top, I think someone has a somewhat tenuous grip on fluid dynamics....... however it would explain why there is so little rain down here in the Antipodes and so much in the UK... :D
This problem is currently a work in progress as I find time to investigate.
So far I have taken the cold start system out of the equation by taking it off and blanking it off. As an aside I noticed that the pistons in the device are closed in the last half mm. by spring pressure rather than the levers that act on them. Despite not having been used for 30 yrs. the pistons also had grooves worn into their sealing faces, presumably from rattling around all that time. Machining the groove off and adding helper springs, (ex Biro pen), made no difference.
More investigation with a mirror and torch showed drips coming from manifold/ O ring joint. ie. running down into the engine and if not for the poor O ring joint probably never to have been noticed.
Taking the top cover off the carb. and raising, with a syringe, the fuel level didn't start the leak again but squirting some fuel into the cavity just forward of the accelerator pump did. I now suspect a poor gasket allowing fuel into an area it wouldn't normally get to and plan to cut another gasket and fit it in the next day or so to see if there is any improvement.
Yes Keith, they do smell a bit which I don't mind.As someone famous once said, "I do like the smell of a hot Elan in the morning", or something like that.

Ralph.
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PostPost by: type26owner » Fri Feb 03, 2006 2:39 pm

http://www.lotuselan.net/forums/viewtopic.php?t=9662
Ralph,
Forget the RTV bit. Just tug the gasket out a little and these new style rubber gaskets will seal the top cover completely liquid-tight.
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