Lotus Elan

Weber leaking

PostPost by: reb53 » Sat Feb 04, 2006 3:28 am

Further developments.
A new gasket made no difference.
Just forward of the accelerator rod is a brass disc, flush with the surface, that acts as a spring anchor. This lifted straight out into my hand, the bottom spring eye missing. I can see the remains attached to a rod down the hole and probably won't be able to remove them and re-attach the spring without removing the carb.
Before I do this can anyone tell me the consequences of not having this spring anchored, and would it give me the symptoms I now have?

Ralph.
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PostPost by: type26owner » Sat Feb 04, 2006 3:54 am

The spring is the internal one to close the butterflies. That's a safety feature and kind of important to have working correctly.
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PostPost by: reb53 » Sat Feb 04, 2006 10:02 am

I will fix it as soon as. Am I right in thinking that it is unlikely to have anything to do with my current problems?

Ralph.
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PostPost by: type26owner » Sat Feb 04, 2006 2:39 pm

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.

Guessing that one float stuck open and it flooded. They must be in perfect working order. You should replace the needle valves and tweak the floats into shape so they don't ever touch the carb body. The fit onto the pivot pin should be closed up to reduce the slop to the minimum. Easier said than done though so be extremely careful! I typically spend an hour apiece on each float getting it perfect. I cannot overstate how important this subject is as I will lecturing about this stuff soon when I connect all the dots filling in the knowledge gap left by John Passini and the Weber Tuning Manual. :lol:

Check the fuel level is 2mm below the sidehole down in the emulsion tube well leading to the auxiliary venturi after reassembly.
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PostPost by: reb53 » Sat Feb 04, 2006 10:15 pm

This problem is slowly evolving.
I initially thought it was solved once I'd taken the cold s. d. out of the equation and after a drive everything was dry. About a minute after stopping, and looking under the carb with a mirror and a flashlight I could see a drip forming under the carb/manifold O ring joint. This continued for several minutes until whatever was acting as a reservoir had run dry.
Lifting the carb against the Thackeray washers had it running out of the other choke as well meaning that wherever the fuel is collecting it has access to both sides.
Both float levels are as good/well adjusted as they have ever been so I don't suspect that but may swap top covers and see if the fault moves.
A bit of gentle prodding on the floats through the top jet cover has them moving up and down quite freely even with a bit of sideways pressure on them to try and make them rub.
I intend to take the carb off today and see if I can learn any more.
Fortunately it's the one nearest the front!
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PostPost by: Dave-M » Sat Feb 04, 2006 10:52 pm

Seem to be norrowing the problem down a bit now.
Are you saying that the fuel is leaking from the bottom of the O rings?
If you are I suggest you take the plenum from the carbs and with your torch and mirror have a look at the pump jets both at idle and after stopping the engine. If they are dripping fuel as I suspect they are you have two problems, both easily fixed.
1) replace your O rings
2) The check valves in the pump circuit are not working as they should.
To fix 1 is obvious. To fix 2:-
Remove carb, remove top cover, remove brass plugs in front of pump assembly one at a time, invert carb and catch brass plunger and ball bearing. If they do not fall out easily you have found your problem as their job is to cut off the fuel to the pump jets after they have done their job, but if they are stuck they will allow fuel in the circuit downstream of the check valve to drip into the carb bore and collect in the grooves either side of the O ring.
If the plunger and ball bearing drop out easily I suggest you reseat the ball bearings to their seats with a gentle tap by means of a tap on top of the ball with a suitable sized punch.
I had this problem a few months ago while trying to balance a pair of rouge carbs. They were slowly dripping fuel into one carb which totally upset the idle on one carb.
When the problem was found and fixed as above normal idle was restored.
Fortunatley its a problem you can actually see so get your mirror and torch and check it out.
Hope the above makes sense
Regards
Dave-M
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PostPost by: reb53 » Sun Feb 05, 2006 10:11 am

I think you may have won the prize Dave.
After taking the carb off and onto the bench I topped it up with gas to the usual level. After a few minutes it started dripping really fast out of one jet and slowly out of the other.
Removing the check valves showed them to be free and clean with no obvious faults. I gave them both a small tap with a punch which has stopped the dripping so I intend putting the carb back tomorrow and seeing what happens.
If the O rings had been sealing perfectly I would never have known it was happening so I intend to give the ones in the other carb a tap as well as it can't do any harm.
I'll let you know what happens once I'm back on the road.

Ralph.
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PostPost by: Dave-M » Sun Feb 05, 2006 11:25 am

Great news my friend.
Regards
Dave
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PostPost by: type26owner » Sun Feb 05, 2006 3:10 pm

Hey Dave,
Have not personally been afflicted with that one yet. Great bit of advice! :idea:

Going to turn my attention to the pump circuit next because John Passini insists they contribute fuel after the intial shot is done at WOT. That does not make any sense to me but I need to confirm it one way or the other.
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PostPost by: Dave-M » Sun Feb 05, 2006 4:39 pm

Kieth, By strange coincidence I have been thinking about the same thing recently, I dug out my old (1969) Passini book a while ago and looked at the notes I made at the time. The reference to pump jet contributing to total flow was one of the things I marked as possibly not correct.
I am now sure it is not correct. The venturi effect around the protrusion of the pump jet is so small it would not be capable of lifting the weight of the check valve and allow fuel to flow into the choke.
Should be easy enough to prove with your wideband Lm1 just datalog a run, solder the jets up and repeat. I would bet there will be no difference.
My understanding of the pump circuit which I use to set up correct operation is as follows.
1) Amount of fuel injected is determined by the actuating rod length of which there are three different lengths. The longer the length the more fuel is injected.
2) The check valve or bleed valve in the bottom of the float chamber is to fine tune the amount injected for a given rod length. ie. it bleeds a percentage back into the float chamber.
3) The pump jet determines the DURATION and not the amount of fuel discharged ie smaller pump jet gives a longer duration of squirt and vice-versa. The amount staying the same and being determined by 1 & 2 above.
It is quite possible to improve fuel economy quite significantly by adjusting the set up providing the the car is driven in a reasonable manner, ie not stamping on full throttle at every opportunity, and opneing the throttle progressivly.
See ya
Regards
Dave-M
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PostPost by: type26owner » Sun Feb 05, 2006 5:26 pm

The venturi effect around the protrusion of the pump jet is so small it would not be capable of lifting the weight of the check valve and allow fuel to flow into the choke.

Exactly! Need to test it though to be conclusive. John Passini could be right afterall and I'm astounded by his work with the tools available at that time. I feel like I'm cheating using an AFM and he only had fuel flow meter. :oops:

There is one other variable you left off your list. Three different piston spring rates are also available. The shot profile is revealed and graphed out with the datalogger feature of the AFM. ALL the really fast stuff is revealed for the first time.

Chatted with Klaus at Innovate Motorsports this week and he said this is causing an explosion of knowledge to happen in the racing world right now. No one knew all the issues without seeing it happen on milli-second level. I got the inside poop on what's coming out later this year. Those folks have it covered, the next device is really cool at a cost I can afford!
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PostPost by: reb53 » Mon Feb 06, 2006 4:46 am

Got the carb back on a couple of hours ago.
Of course what works great on the bench doesn't necessarily work out on the road, and this was the case in this instance. Still dripping away a minute or two after stopping. It's a long week-end here, with my O ring shop closed, so I didn't replace those. After all, they are not causing the problem, merely letting me know it exists.
As I'm getting behind on revenue earning work this problem is going to be put on hold for a while.
Next step will be to investigate the seat that the ball bearing sits on and maybe make a little cutter to clean it up. Just like an engine valve a fine line contact will make for a better seal.
Will let you know when, or if, I find an answer.

Ralph.
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PostPost by: Dave-M » Mon Feb 06, 2006 9:26 am

Ralph, Just a quick thought, You do have the small aluminium washers on the pump jets dont you? And the rubber O rings are present under the pump jet covers? Either of these will cause a leak if they are not 100%
Regards
Dave
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PostPost by: reb53 » Mon Feb 20, 2006 5:20 am

Finally got back to this problem after a bunch of family crises all came at once. And yes....I should get my priorities right, after all I've had the car longer than I've had the family!
The O rings sealing the jets are new as are the little aluminium washers.
The ball bearings seat onto brass which looks fine.I gave it a touch up with a small cutter to no good effect.
I'm beginning to think that I should simply replace the large manifold O rings and I'll never see the problem again as the leak will never show itself and simply run down the inlet manifold.
As they say "ignorance is bliss" but I still want to know what is going on and plan to take the carb. off again when the car is laid up for the winter in a few months time.

Ralph.

P.S. For all you old car nuts out there ....just saw a genuine 1930s "Squire" out on the road. (7? made).
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