At Last

[Charlie Chops 1940]

Those of us that are old enough to know that points were the only thing available, if the carbs are right, it still runs fine.  

Hey Charlie you're not old enough

Maybe that's it! I know there was no offense meant, and there was none taken.

Charlie

[Bruce Dorsi]

I've already got lots of bucks in the Weber carbs and they are way fat.  I will keep exploring before I fully give in. Most of the literature I read on Webers point towards improved ignition systems, and my Weber guy isn't trying to sell me anything. He's just offering what he feels needs to be done before we start rejetting the carbs, if necessary.

If anyone on here has any real world experience with side draft Webers I'd sure like to hear your story.

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There is no doubt that having good ignition is important, but most stock ignition systems will produce a good, strong spark up to at least 4000 rpm.   .......At higher rpm's, the ignition system may need some help.   .......Many sbc's have  turned 7000+ rpm's using single-point distributors with stock coils.  

I'm sure you realize that the distributor must be in good mechanical condition to prevent erratic timing or spark flutter.   ......The correct ignition timing curve helps wring out the most horsepower.   ......Good-quality plug wires are a must!   .....The timing chain must not be worn or stretched (if your engine has one).

That said, if your engine is not running right under 4000 rpm, your problems are not likely in the ignition system.

My only experience in tuning a Weber, was a complete disaster, despite receiving lots of advice from respected sources.   .......This took place pre-internet days,  so there was not a lot of info available.  Then, as now, it was difficult to sort truths from hearsay.

I installed a  turbocharger on a 95ci Lotus 4-cylinder, which was actually a 1600cc Pinto block, with a Lotus-made head having dual overhead cams.  ......I removed the two stock Stromberg constant-depression carbs, and plumbed one Weber 45DCOE to the turbo.  ......I can assure you that I had no ignition issues, yet I could not get the carb tuned correctly.  ......I was running so rich, that I eventually washed all the oil from the cylinder walls, requiring my nearly-new block to be bored and fitted with oversize pistons & rings.

According to everything I read, or was advised, at the time, this carb and the base jetting was supposed to be close to optimum.  Not so!  

I used an ehaust gas analyzer which was strapped to the rear bumper, and provided on-the-road readings.   .....I became very proficient at doing engine cuts and plug reading on the shoulder of the interstate.  

No matter what I tried, I could not get this Weber tuned to my satisfaction, although I was able to make improvements from its base jetting.

After needing  the oversize piston & rings,  in frustration I removed the Weber and installed one of the original Stromberg 1-3/4" constant-depression carbs.  ......The carb swap was succesful and required only slight tuning of the Stromberg.  .......The engine would run 7-8 psi boost, and run up to 7500 rpm, with no problem!

Along the way, I did learn a few things about Weber sidedrafts:

(1) DCOE's are very sensitive to fuel pressure, and require a reliable low-pressure regulator.  Pressures in the 2 psi range are all that is required, but I don't trust my memory on that number.

(2) DCOE's do NOT like to be mounted rigidly to a manifold.  Almost all succesful installations utilized spring-loaded mounting on resilient gaskets.

(3) DCOE's are sensitive to the angle at which they are mounted.  The angle affects the fuel level in the bowl, which in turn, affects the emulsion tube selection.

(4) There are enough variables on a DCOE to cause you to chase your tail, if you make too many changes at one time.  .......You have to contend with venturi sizes (choke tubes), main jets, idle jets, emulsion tubes, pump jets, etc., and if you change too many variables at once, you can easily head down the wrong path.

(5) Weber carbs look impressive, and if set up properly, can rival mechanical fuel injection in performance.  

(6) Weber parts were expensive, and I spent more $$$  for jets, tubes, gaskets, etc,  than I did to buy the new carb!

I hope you are more successful than I was!

What size are your Webers, Charlie?

[Charlie Chops 1940]

Bruce,

1) Lots of good points in your response. I have not addressed the fuel pressure yet but intend to order a guage and regulator this weekend as I suspect the stock pump is delivering more than the 3 psi or so that I have seen published as best. Obviously I haven't finished my homework on this issue.

2)I have the carbs mounted with the silicone/steel O-ring "gaskets" with the appropriate rubber grommets and springs. Good point though.

3)My carbs are at about 7 degrees up which is  just within parameters I have found. I modified the intake to tip up after all the hood parts and supports were made and I found the carbs wanted to go right  through the
top of the hood sides and supports.

4)I have one Weber book and a lot of printed material from the web and corrected a number of small issues getting to this stage. I appreciate the admonitions not to change too many things at once. This project has made me pause and reconsider a lot of data.

5)Yeah, they do look great and given that they are so physically integrated into this car I'm committed to continued analysis of the system and subsystems.

6)The carbs are 45 DCOE-152's and seem to fit all the sizing charts for a 2.6L engine with 160-180 hp.

I'm not anxious to throw in the towel on the points dizzy. The unit is freshly rebuilt, but the coil is an unknown out of inventory. I'm using Taylor 7mm wires, properly crimped. I will be replacing the coil.

This engine is a perfect example of getting all the subsystems up to snuff in a fairly high state of tune unit...10:1 forged pistons, ported and port matched head with bigger valves and springs, .480 lift cam and a capable induction system.

It may take a little while but I don't think throwing a catalog of parts at it are indicated just yet. I'm an old drag racer and if there's one thing I learned in that pursuit was to change, document, and test as few thing as possible at a time. Maintaining the resolve to do so is tougher, but I have a lot of patience.

Charlie

[Bruce Dorsi]

More questions, Charlie:

Are you using an individual-runner manifold, or is there a plenum under the carbs?


If there is not a common plenum, is there any sort of balance tube or passage between the individual runners?

The two best Weber books I could find at the time were written by John Passini.  ...One book was devoted to Weber theory, and the other was devoted to tuning.  ....I don't know if these books are still available.

[Charlie Chops 1940]

More questions, Charlie:

Are you using an individual-runner manifold, or is there a plenum under the carbs?


If there is not a common plenum, is there any sort of balance tube or passage between the individual runners?

The two best Weber books I could find at the time were written by John Passini.  ...One book was devoted to Weber theory, and the other was devoted to tuning.  ....I don't know if these books are still available.

The manifold is a Clifford unit which is what I would call a 4 into 2 style as the head has only 2 ports, so each 2 carb runners feed a common runner at the head. Think of it as 2 manifolds connected at the carb base flange. The intake did not have a balance tube so I fabricated one from 1" diameter aluminum tubing and had it welded in. The decision to do this was based on information from Weber users who did so to balance out their system. Good, bad or indifferent it's there now. My gut feel is that it will be beneficial.

I haven't seen either of the Passini books anywhere. I have one by Pat Braden and a ton of data gleaned from the web.

I did find a Pertronix electronic conversion kit for my dizzy at a fair price....waiting to see if it is new before I buy it. In fact the guy has a couple so I'll probably buy both.

Charlie

[Dirty31]

Too Cool!!!!