Weber Mainstack

[type26owner]

I've got some pdf pictures of the Weber mainstack to explain how this stuff works but I can't get them to appear here with a URL link. What file format is best? Bummer!

First off the standard way to set the fuel level is inherently unreliable. Setting the floats to a gap from the cover in an indirect and rather poor way to do it. Think about this a second the floats' buoyancy is what determines the fuel level not this magic gap. The gap will set the fuel level too high anyways (24mm). Blindly doing it this way puts the fuel level in the mainstack jetting well to just one millimeter below the passageway leading to the auxiliary venturi (23mm). This is close enough to spilling over the edge that it does so when ascending or descending a steep grade or when accelerating or braking. Best practice I've found is to set the fuel level so it's two millimeters (25mm) below the passageway and to do the measurement by direct means. While the engine is idling I remove a mainstack assembly and insert my homemade pipette into the well and measure the fuel level with a scale. This eliminates all the play in the pivot pin and buoyancy and the structural pliability errors of the floats. This pretty much eliminates the popping and backfiring on overruns from #1 & 3 cylinders and the fat bog on #2 & 4 cylinders on acceleration.

I'll add more info to this posting later.

[type26owner]

Tried to review some of my earlier postings and found the search capability of this forum totally sucks. I had to view the whole list of postings I've made and then when I opened one up and then wanted to go up in time to the next subject posting I couldn't, it popped me back to the top which is present time. This is not what I call user friendly at all. I posted this stuff here to have a record of it. Now I find it's useless even for my purposes.

Hey Jeff, is this a permanent feature?

[Elanman99]

Keith

I can't wait to see the PDFs (or whatever you end up using) as it might help my poor brain get some idea of what you're trying to do. In addition please could you explain what 'Fat Bog' and 'structural pliability errors of the floats' mean in plain English.

Ian Phillips

[type26owner]

Hi Ian,
http://www-eng.lbl.gov/~franck/Car_Stuff/weber_well.pdf
http://www-eng.lbl.gov/~franck/Car_Stuf ... _level.pdf

The 'fat bog' is the result of having the fuel level too high and it gushing over the edge on #2 & 4 cylinders when you're accelerating hard. The lefthand well shows the typical fuel level if you set it to the factory specs. Quite clearly you should be able to spy the problem here. The fuel level in the well will try to stay at the same level as the fuel sloshing around in the float bowls. This is not rocket science stuff.

The structural pliability is built into the floats due to the design. The float assembly is delicate, flimsy and easily warped out of shape. The density of the fuel and the pressure from the pump all input small errors in the ultimate height of the fuel level so setting it by the indirect method is just asking for it be wrong.

What's really important is to not let the fuel level get too low either. Too low is uncovering the four lower holes penetrating into the air corrector cavity of the emulsion tube. Those four holes are the ones which feeds air into the fuel and creates the stream of bubbles which lifts the fuel as it mixes into an emulsion. The fluid properties of the emulsion are subject to two-phase flow behavoir and this is were this stuff does get complicated. Not knowing about this type of flow will hinder you.

[Elanman99]

Keith

I agree with you that the workshop manual method of setting the fuel level is rather suspect, but its probably OK if all the relevant parts are within tolerance. All the potential problems you outlined are surely dimensionally insignificant when compared to the temperature, vibration, surface tension and all the other things going on in that little pot.

I do not have the manual to hand at the moment but where does the 23mm dimension come from? BTW both PDF links seem to show the same (Solidworks?) picture.

Ian Phillips (I want fuel injection really!)

[type26owner]

Ian,
I'm filling in the technical info holes that all the others that have written on this subject but have left the crucial stuff untold. Why would they do that is the real question? Sad to realize how many of those folks are really posers afterall. I know better then to blindly believe what's been written before without testing to confirm their shit and mostly it's been a bunch of bull. You're doomed to never be innovative if you operate in a mode that does not question everything. If you simply do as I'm telling you without the arguing, you'll most likely get your Webers tuned to a level nearly equal to what fuel injection will do with the least amount of fuss and bother.

The 23mm is the distance from the top of the carb body to the lower edge of the passageway leading to the auxiliary venturi. That lip is super important because accelerations will cause spillage at the wrong times and the vacuum signal via the jets is tuned to overcome that tiny force of column head pressure of just 2mm.

[type26owner]

Mike Ostrov has asked me to give a technical seminar on the finer points of Weber tuning at one of his Saturday gatherings. Unfortunately, due to a family reunion I cannot make the scheduled one in July. For you folks in the Bay Area who are interested I'll try to be at the following one though.

My webers are happy to idle at 700 rpms now with the present settings. I suppose I should also reveal I add a vicosity modifier to the pump fuel. Their claim about the fuel mileage increase is over the top as far as I can tell but it definitely does help suppress the knock. This adds about three extra points to the octane so I can just barely get away running 34 degrees of total advance while using the 91 octane pump fuel. Keep in mind the advance values stated in the manual are from the distant past when 100+ octane fuel was plentiful. Man, I tell immediately when I get ripped off now with substandard fuel.
http://www.apdinc.com/GTAfuel.html

[type26owner]

Realized with my new rev limiter I can now accurately measure the vacuum signal from the auxiliary and main venturis for the first time at WOT.

Not going to waste my time posting anymore Weber tuning stuff here. Going to find a better place where all the info can be found easily.

[gjz30075]

Keith,
Be sure to tell us where you're going to post so we can follow.
Thanks for the great info,

Greg Z
'72 Sprint

[type26owner]

Hi Greg,
It'll probably be on one of the other Lotus websites since the owner of this forum does not respond to me ever. Wait until you read what I've done. I managed to figure it out all the way where no one has gone before apparently. Should be easy for anyone with average skills and the correct tools to get the Webers running to perfection. Right now I get to exclusively enjoy my Webers that are behaving well past my highest hopes. Screw the fuel injection! I'm keeping the Webers.

[type26owner]

Hey Greg,
Do this simple experiment which is perfectly safe as long as your float bowl level is not set too high. It takes all of 5 minutes to perform. Remove all the emulsion tubes from the carbies and go drive the car in a no traffic setting but bring the jetting along with a screwdriver. You'll experience exactly the rpm range and torque limit of the progressive holes circuit exclusively. Try and climb a slight incline in first gear. Notice how much throttle motion you're using too. Hint: the engine will die as soon as you rotate the throttle plates past the holes.

After doing this test you'll know how much to trust all those that gave advice concerning tuning the DCOEs. They should all be fitted with glass belly buttons.

[gjz30075]

Keith,
Right you are. Thanks

Greg

[type26owner]

Since I'm a rookie at publishing any automotive articles I contacted Jon Rosner who's part of the GGLC and in the publishing biz. He suggested that I make a video of the tuning process so folks could actually see how it's done along with an article. Hadn't thought of that. Kiyoshi, does the GGLC website have enough bandwidth for a ten to twenty minute video?

I'm going to render obsolete virtually everything that's been written about the DCOE Webers up until now.

BTW, I'm fairly certain I can get almost any Weber equipped car to pass the California smog test as long as you add a cat.

Only problem is I lack the weight of enough statistical numbers to really support my theory. I've only tuned my Elan and my brother's Super7. I need a few other cars to tune up. Perhaps I could do this for some lucky Lotus owner realtime at one of Mike Ostrov's tech seminars.

Your car must be in good condtion as far as the ignition system goes and the exhaust system must not leak all the wayback to the tailpipe. I will not work on any car that has been neglected by letting all the airleaks go unrepaired on the induction system. The leather seals on the throttle spindles must be new and the center coverplate that protects the accelerator pump lever assembly on the throttle spindle must be air-tight. I'll add the seals to go on your idle mixture screws for free. Lastly the balancing linkage between the cabies wears out underneath the adjustment screw by wearing a pocket due to fretting. That must also be repaired beforehand.

[marcfuller]

Keith, I would buy your video! (Heck, I would even do the video and editing on spec. Wish there was less distance between CA and CO) Great idea and good luck!

Regards, -Marc

[mac5777]

Keith, I will be at Mike Ostrov's next tech seminar on the 16th of this month. I took 1st place in the S3-S4 glass at the WCLC meet at Tahoe, with my just rebuilt/restored 67 S3 elan coupe BRG. And if you want to use it as a weber demo, at that time, it is available. I think I meet all of your requirements. If I'm the lucky one I'll bring a video cam. If you can not be at the next Ostrov meeting, let me know and we can do the video for the other elan owners at a later time. Let me know when.
Thanks, Sarto
67 elan coupe S3
36/5785