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