tuning and sync-ing 3 webers. . what's the process?

[Anonymous]

well. . . i know how to tune one weber . . . but now i have three set up with non-progressive linkage.

do i set all the idle mixes one at a time or set the center and just match the other two the same number of turns on the mix screw.

to set idle speed do i need a uni-syn contraption? it is for idle speed right?

any advice on the order and procedure to do this?

 

[Anonymous]

Sorry I don't have any answers on this as I'm getting ready to do the same thing only with diff carbs.
I've been thinking about putting cover plates on the two out board inlets and then installing & adjusting each carb on the center one at a time.
Has anyone done this or is it just plain foolish to move them around this much?
My logic was to get each operating at optimum performance by it self and then put all three on and work only with the linkages.
Thanks.
DaveP

 

[Anonymous]

It shouldn't be that complicated. . . . anyone?

 

[66200i6]

Non-Progressive?

I would start with the same process we used on the dual two-barrel Weber VW engines. There may be a difference in the fact that these three carbs are mounted on a common manifold where as the Webers on the VW were independent manifolds.

In a nutshell when the throttle cable/linkage is moved the action needs to be transferred to the throttle linkage of the subject carbs equally. This could all be done easily enough mechanically but this result is not necessarily what you want. When that throttle is moved, what you really want to happen is that equal amounts of “Air Flowâ€￾ move through each of the carb ventures at the same RPM readings idel, cruse and a selected upper RPM.

With the VW’s we used what is called a Sync Meter. This meter fit the air horn of the carb and allowed the airflow to pass through to run the engine while providing an indication of the amount of airflow entering the carb throat. There are also meters that are made for the cycle industry that uses the ported vacuum to provide a signal to the meter that represents the airflow.

So the rub is to adjust the linkages to the three carbs to a point that at different RPM levels the airflow to each is the same. Start with the linkage disconnected. At idle (500-800?) each carb needs to flow the same amount of air. Then install the linkage so after installation the airflow through each carb is not change from your first adjustment. If there is a change in airflow make sure that the change is the same at each carb. The fine-tuning happens next by setting the throttle at the input (pedal) to make sure that all parts of the linkage are being used. Take the RPM up to a comfortable level say 1500. While the engine is maintaining this new RPM setting check your airflow through the carbs. If there is a difference the adjustment must be made at a point in your linkage that affects that carb only. This process is followed until all three are reading the same airflow at this RPM. Drop the RPM to idle and confirm the airflow at each carb is the same.

That is the general idea. It may sound involved by with practice it doesn’t take long.

Good luck, Ric.

 

[Anonymous]

thanks for the response. . .

that clarifies how to synchronize the throttle set-up.

But how about setting the mixture screw . . . do you just do one at a time . . . . .with the usual "low rpm and back out the screw until it runs best" trick?

or some other method. . . hopefully short of swapping them all to the center position to set the mixture.

 

[Anonymous]

I would think with them all working together you would procede as follows.
1st ---make sure all carbs have their throttle plates closed tightly when speed screw is backed off. Then turn the screw back and forth till it just barely closes.
2nd-- screw each screw in maybe a 1/4 - 1/2 turn.
3rd-- install carb and hook up linkage
4th-- set each mixture screw in the same location, maybe1&1/2 turns out.
With all 6 cylinders having access to all 3 carbs at once I don't see how you will be able to do any individual agjustments.
If you had the manifold separated into 3 chambers where 2 cylinders were isolated to individual carbs a vacumn port could be drilled in each chamber and synch'ing with 3 vacumn gauges would be a fairly simle thing. But as it is, the entire log is availagle to every cylinder at all times. The bad side is a vague tuneing reaction to carb adjustment--the good news is fine tuneing shouldn't be as critical. Just make sure all carbs are opening dead evenly and that all carbs are jetted and adjusted identical. What ever you do to 1 carb, do to all the carbs. which means make very small changes every time as the reaction will be 3 times what it would be on 1 carb. The biggest problem is that when stepping on the gas you have a lot of venturi and flooding may be easy but if you can adjust your foot -it may work well. Also vacumn will likely disappear in a hurry at lower rpm's in reaction to throttle opening('s). You have in essence a very long 3 barrel carb not 3--1 bbbl carbs this way.

 

[JOHN G]

I have the setup and I would put on the progressive linkage-the fuel dumping will be enormous and getting it to idle will be difficult withoout putting in some really small idle jets. Email me if ya want the rundown of what I've done so far.

 

[Anonymous]

actually, i ran it progressive for a year or so. . . then took it to my inline six guru . . .

and he set it up non-progressive. it runs so good this way and has such great off the line power that I don't want to go back.

the problem now is that he is out of the business and i need to maintain the tune that he put on it.

 

[LaGrasta]

Todd's out of business?

 

[Anonymous]

Ok i'll try to help out how I can

I got Twin Webers on my little Sunbeam, unlike VW's the carbs all sit on the same manifold. I used a Vacume testing tool I cannot remember the name of it currently. But you stick it over the throttel bore one at a time and it has a tube with a small ball that floats in it, you play with the mixture on every bore till each and every bore gives you the same reading. (a time consuming task, as when you change one, you have to go back and work on the one you already did.


As for openening them on a non progressive throttle, I can give you an idea of what i did by posting a picture of it. It may help you to get an idea of how to modify or make a linkage. That may not be the exact same carbs but the prosscess should be similar.


The main diffrence is that you run with one plane While I run this on indevidual runers per bore. However the idea SHOULD be the same... I think

good luck

 

[Anonymous]

Todd's out of business?

Todd Fields is not out of business. . . as far as I know he is still selling brake kits, but I think he is too busy to do mechanic work at the moment. If I had a million dollars I'd pay him to hang out in my garage all day. The guy did some really great work on my car.

The only problem. . . . is that he set a standard with his tuning that I am having a hard time maintaining.

 

[LaGrasta]

Sounds like you're satisfied with the top AND bottom rebuild he did. It's too bad you did it seperate, but hind sight is 20/20.
I remember Todd saying somehting about the mock silencers you arranged on your exhaust tips. Was that the main reason for the problem?

 

[Anonymous]

to all- thanks for the responses-

after checking everything out i am thinking i have a vacum leak since turning the screrws seems to produce erratic results.

1. when i cover the center carb with the uni-syn or even my hand . . . the idle goes UP! doesn't that indicate a giant vacum leak somewhere?

2. the classic sign of the wandering/cycling idle

3. o-rings never last more than a year anyway, right?

so i'll have to pull it apart and re-set the manifold and try again.

Anymore theories would be appreciated

I will figure this out. . . I have to.

La Grasta- on the exhaust- that's todd's theory. . . my urge to try new ideas out sometimes gets me in trouble. . .i'd also add that it's hard to hear pinging over open pipes. . .

live and learn, right?

Now I have a "normal" exhaust system and enjoying just making my car run the best it can . . . I found other projects to execise my creativity on these days.