Lotus Elan

Weber Carb Flooding During & After Cornering On Race Track.

PostPost by: mojoluthier » Tue Sep 05, 2017 7:18 pm

This is precisely what I suspect. I did not build the engine and have not measured duration, but do know the lift is well above standard. It idles surprisingly well at 850rpm considering. And I have mused that the cam is perhaps therefor off timing a bit. I really don't want to pull and disassemble the engine as I have gotten my jollies with three seasons of AutoX and at 70, am indeed ready to move on. The manifold, by the way, is a Redline intended for this purpose. I do have the carbs rubber mounted.
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PostPost by: mojoluthier » Tue Sep 05, 2017 7:22 pm

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PostPost by: davidholroyd » Tue Sep 05, 2017 8:15 pm

Plastic floats and spanish carbs are to be avoided
Last edited by davidholroyd on Wed Sep 06, 2017 3:58 pm, edited 2 times in total.
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PostPost by: mojoluthier » Tue Sep 05, 2017 8:22 pm

Sadly, I did remove the entire cold start mechanism from my first set of carbs and put on plate covers to no effect! That was Dave the lotus guy's recommendation. Also, he set my plastic floats not to between 12 and 13 mm, but to 12.7 mm, which was amusingly anal. That didn't do it either.
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PostPost by: Esprit2 » Tue Sep 05, 2017 9:09 pm

mojoluthier wrote:I have tried 4 different air horns with similar results, including cutting up a set of Weber horns and using lengths from 1 to 6 inches!

I have replaced my carbs with $850 worth of brand new Spanish mades.
Use ten different lengths... it doesn't matter. The 'air horn' part that sticks out beyond the end of the carb body is only for tuning for power at different rpm. It has nothing to do with holding the carb together, clamping the aux. venturi & choke in place, or preventing leaks.

It's the spigot sleeve below the mounting flange that actually slides into the carb throat that's important... and it only comes in one length "IF" you're using Weber air horns. I've seen some people bolt Dellorto-style, flange-mount air horns onto Weber DCOEs, and that?s a mistake that can lead to fuel leaks.

So back to my question, which style of air horn do you have installed? Weber sleeve mount, or Dellorto flange mount?

You can spend twice that amount on carbs and parts. But if they're not installed correctly, they won't work right. At what point are the carbs the victims, not the culprits? Find a carb specialist who knows what he's doing with DCOEs. In this modern fuel injection age, that may not be every corner mechanic. Find an old guy.

mojoluthier wrote:I have purged my fuel system, used 3 different fuel pumps, and have an inline pressure regulator at 3lb, according to the gauge I installed.
As I noted before, Weber DCOEs like 1.5 to 2.5 psi. 3.0 psi is too much. Not by a lot, but it's too much. Carbs are sensitive, and they need to be set-up accurately. Close but not quite won't produce results with which you'll be happy. Given your fuel leak problem, I wouldn't accept any not quite right settings that could negatively affect fuel leakage... like excessive fuel pressure.

mojoluthier wrote:The fire, when it happens, is apparently from fuel outside the horns, not on the body itself.
(Snip)...
This happens only on extended right hand turns.
"From fuel outside the horns"... what do you mean? I don't follow that.

Are the carbs on the right side of the engine?
And they leak in long, high-G right hand turns?
Remove any air filter backing plate so you can see the naked outer face of the carb body. Notice the large diameter hole just above one throat/ air horn. That's the float bowl vent. The Air Corrector Jets suck air from within the float bowl, and the air enters through that vent hole. There's a direct passage from that vent hole to the float bowl. If the fuel level is too high in the float bowl, then high-G cornering can conceivably result in fuel making it out of the vent. In that case, it ends up inside the airbox/ air filter (unless you're running individual air horn 'socks), soaks the bottom side of the filter element, and leaks out. Sound familiar? Check that out.

What's the float height (aka fuel level) set to?

mojoluthier wrote:I have hired to different pros to assist me. One owns a local lotus centric race shop, and the other has a long term business at the local Sonoma Raceway.
There are a lot of modern 'Lotus Specialists' that can tell you all about fuel injection, feedback loops, mapping ECUs, Turbos, boost controllers, and Toyota 2zz motors, but they know jack-sh? about carburetors. Are your pros 'carb' pros? I suspect not if they haven't been able to set-up a pair of DCOEs yet. DCOEs have been around since shortly after the Ark landed. Find an old guy who knows carbs... better yet, DCOEs. He won?t need computer diagnostic equipment. He?ll use a manometer, a screwdriver, and some smarts.

mojoluthier wrote:My local club, ESCA, has been unable to brain storm this and prefer I don't participate due to fire hazard, and I can't blame them.
They can't because they clearly don't know carbs and or DCOEs. Asking someone who doesn't know something over and over and over again isn't going to get you the right answer. Find the old 'carb' pro, preferably an old 'DCOE' pro, and ask him once.

Besides his obvious talents, Einstein was also a very wise man. One of my favorite Einstein quotes relates to his definition of insanity. It's "Doing the same thing over and over again, always expecting a different result".

Best of luck,
Tim Engel
Last edited by Esprit2 on Tue Sep 05, 2017 10:12 pm, edited 3 times in total.
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PostPost by: Esprit2 » Tue Sep 05, 2017 9:16 pm

Here's a picture of a Weber DCOE 'sleeve-mount' air horn. I snipped it from the Eurocarb website.

Note the raised flange around it's waist. The portion below that waist flange slips into the carb's throat, and pinches both the auxiliary venturi and the choke in place. Look up an exploded parts drawing for an illustration of how that all fits together. The airhorns are not just optional embellishments like they are on Dellortos, they're required parts of the Weber carb body.

A Dellorto-style flange-mounted air horn stops at that waist flange... there is nothing below the flange. Using one of them on a Weber DCOE doesn't work, and can lead to leaks.

Regards,
Tim Engel
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weber-dcoe-trumpet-aka-air-horn-note.jpg and
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PostPost by: Esprit2 » Tue Sep 05, 2017 10:31 pm

Go here:
http://tinyurl.com/yavlpxz6
Near the top-center of the page, below a bunch of red option-link buttons, click on "View Diagram". That will bring up an exploded parts diagram of a Weber DCOE. Check out the air horn, auxiliary venturi and choke in the upper right corner. The spigot sleeve portion of the air horn below the waist flange shoves the other bits down the throat, and clamps them in place.

The attached JPEG is an example of the Dellorto-style flange-mount air horns that do not work properly on Weber DCOEs.

Regards,
Tim Engel
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dellorto-dhla-trumpet-aka-air-horn-217kb.jpg and
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PostPost by: mojoluthier » Tue Sep 05, 2017 10:51 pm

Not as shiny as yours,Tim, but yours hasn't been on fire :? .

Image

My point is that these are standard horns and all others I used have had the Weber specific skirt as well. This can be seen by the way they attach.

I admit to be surprised at your quickness to assume I am dealing with non-traditional modern upstarts as opposed to people who have a grip on carburation, and DCOE Webers in particular. My lotus connection is Dave at Veloce Motors, quite well known despite their low profile. My Infineon (earlier but superior name) connection is Robert McCormick and while he is actually best known as a chassis man, he at the least had the right tools and a full range nearly complete jetting set. Many people in ESCA (celebrating its 53rd year) have traditional machinery and were alive when it was contemporary, as I was. No, no expert Weber person among them (I might get there), but terrific resources.

None the less, I appreciate your willingness to share. In as much as I AM feeling defeated, and DO have the car on the block, I guess I am sort of hoping for a magic bullet from the blue. I truly believe that as long as a buyer is not going to race the car, they will never encounter this fly in the ointment. Of course since it IS a race car . . .
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PostPost by: Esprit2 » Tue Sep 05, 2017 11:27 pm

It wasn't my intent to insult your mechanical resources. But no matter how good they are as generalists, or in their own specialties. after all the work and time you've described going into your carbs, they've not yet gotten them running correctly. To me, that says they're not carb guys, or specifically, DCOE guys. It's kind of hard to paint that any other way. I doubt that their feelings would be hurt if you were to seek out a DCOE specialist.

There's a old-guy dyno shop near me. The guy knows DCOEs and has bins of jets and parts on hand, so changes are plug-n-play rather than order-and-wait. Take your Weber carbed engine in to him, tell him what you want (economy, flexibility or power), and get out of the way. He'll put it on the chassis dyno, hook up a 4-tube manometer, and a tail pipe sniffer. When he's done, it's right. You need to find one of him, and the resources you've mentioned don't seem to be able to do what he does. They're not bad because of that, they're just not who you need.

Regards,
Tim Engel
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PostPost by: prezoom » Wed Sep 06, 2017 1:08 am

Even with the clamping forces of the air horn, it may not be enough to prevent fuel leakage from the transfer port to the aux venturi, which will result in excess fuel around the outside of the air horn. What I have done is reinforce the P clip that pushes the aux venturi against the carb body. I did this by cutting a small circle of rubber from a flat sheet, and inserting it inside of "P" of the clip. This makes it very difficult to remove the aux vernturi. Along with this, I cut a strip of the same rubber and placed it in the slot that is cut in the body that is along side the aux venturi and the air horn. Then I installed a small diameter O ring around the air horn and seals the air horn to the body. I now have no fuel leaks, and do not worry about spurious sparks from the distributor igniting leaking fuel.
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PostPost by: StressCraxx » Wed Sep 06, 2017 2:13 am

mojoluthier wrote:Not as shiny as yours,Tim, but yours hasn't been on fire :? .

Image

My point is that these are standard horns and all others I used have had the Weber specific skirt as well. This can be seen by the way they attach.

I admit to be surprised at your quickness to assume I am dealing with non-traditional modern upstarts as opposed to people who have a grip on carburation, and DCOE Webers in particular. My lotus connection is Dave at Veloce Motors, quite well known despite their low profile. My Infineon (earlier but superior name) connection is Robert McCormick and while he is actually best known as a chassis man, he at the least had the right tools and a full range nearly complete jetting set. Many people in ESCA (celebrating its 53rd year) have traditional machinery and were alive when it was contemporary, as I was. No, no expert Weber person among them (I might get there), but terrific resources.

None the less, I appreciate your willingness to share. In as much as I AM feeling defeated, and DO have the car on the block, I guess I am sort of hoping for a magic bullet from the blue. I truly believe that as long as a buyer is not going to race the car, they will never encounter this fly in the ointment. Of course since it IS a race car . . .


Hello Mojo,

Have you spoken with Keith Franck of Martinez? He runs a yahoo groups message list called sidedraft central. PM me if you would like his contact info. He does tuning, troubleshooting and problem solving of all things DCOE. He is worth a try.

Dan Wise
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PostPost by: rgh0 » Wed Sep 06, 2017 10:59 am

prezoom wrote:Even with the clamping forces of the air horn, it may not be enough to prevent fuel leakage from the transfer port to the aux venturi, which will result in excess fuel around the outside of the air horn. What I have done is reinforce the P clip that pushes the aux venturi against the carb body. I did this by cutting a small circle of rubber from a flat sheet, and inserting it inside of "P" of the clip. This makes it very difficult to remove the aux vernturi. Along with this, I cut a strip of the same rubber and placed it in the slot that is cut in the body that is along side the aux venturi and the air horn. Then I installed a small diameter O ring around the air horn and seals the air horn to the body. I now have no fuel leaks, and do not worry about spurious sparks from the distributor igniting leaking fuel.


This is one of the reasons I prefer using 45DCOEs in a race engine as the venturis are fixed in place by a locking screw rather than the spring clip which reduces the leakage issues

cheers
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PostPost by: Chancer » Wed Sep 06, 2017 11:57 am

For those of you dedicated enogh to resolve all the leaks and potential leaks from your Webers if you now are feeling at a loss and missing the challenge then swop them for a set of Spanish made Webers and you wont be lacking any more, you will have to seriously up your game though.

If the OP's problem does prove to be the float chamber vent into the air filter housing then you could block the vents and use the castellated vent washer that fits Under the jet cover on early Webers, I would not want to be in your harness though if you turn the vehicle over. :shock:
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PostPost by: Craven » Wed Sep 06, 2017 3:28 pm

Readers may be interested in these pictures, they are, I believe, of the last design of 40 DCOE carb?s to be made by Weber in Bologna .
Note.
The auxiliary venturi are held in place by a locking screw from beneath and not a clip.
The Air Horn fitment is as Dellorto.
There is air bypass adjustment, under white caps.
Also has points for nanometre attachment.
O ring fitted to the idle circuit adjustment screw.
It would seem this is the design taken over by the Spanish.
Regards.
149.jpg and

149-ch.jpg and

40-aux.jpg and

air-horn-weber.jpg and

web-149.jpg and
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PostPost by: mojoluthier » Wed Sep 06, 2017 5:46 pm

Now I am learning things! I did suspect that the problem lay in the Spanish version, most people I know use earlier Italian Webers. Thanks, folks.
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