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Discussion Starter #1
I recently had my weber carburetors rebuilt by someone however after installing them on the engine and attempting to balance them using my Synchrometer, I've gotten differing airflow readings between barrels from each carburetor. I did the best I could adjusting the screw that balances the two carburetors to each other. That in itself is irrelevant since the airflow difference is within each carburetor.

In other words, reading the barrels from left to right with the carburetors installed on the engine, I'd have a reading from cylinder #4 barrel at 7 kg/h while cylinder #3 barrel has a reading of 4 kg/h. The other carburetor cylinder #2 has a reading of 4 kg/h and cylinder #1 had a reading of 3 kg/h. To balance the carburetors, I adjusted the screw to balance airflow between #2 & #3 cylinders; both reading 4 kg/h.

I tried adjusting the "butterfly" plates on the carburetors thinking that was the problem but that didn't make any significant difference. ,
I've never had this kind of problem syncing my carbs prior to the carburetor rebuilds and I'm at a loss.

Any thoughts or suggestions would be greatly appreciated.

Thank you . . . 808Alfa
 

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I tried adjusting the "butterfly" plates
That is usually not a good idea. Maybe Gordon Raymond will chime in on that.
 

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Discussion Starter #3
Thank you "alfaparticle" . . . I'm no worse off after adjusting the plates. The airflow readings were basically unchanged.

If there are any other comments that might point me in the right direction that would be appreciated. As you state, hopefully Gordon Raymond may have some.

Thank you . . . 808Alfa
 

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First of all, I detest synchrometers for balancing two (or three) carbs. However they can occasionally reveal when a non-experienced person has twisted your throttle shafts, bent your plates, or something worse.

Depending upon the value you place on your time, ask Gordon if he’s got an open slot, and send him your carbs to be straightened out.

Sometimes the most expensive route is the one that costs the least, and vice versa.
 

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Vacuum leaks? #4 especially could feed a leaky brake servo. Try plugging the line and measure again. Same for #1 on some later manifolds that have a provision for vacuum advance.

I like to initially balance the carbs by removing the inspection plugs covering the progression holes; aiming a flashlight at each port and fiddling with the idle speed screw (engine off) will let you see the edge of the butterflies in relation to the progression holes. A twisted shaft on either carb will be evident.
 

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But Mad North-Northwest
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You don't say what sort of Webers they are, but if they're emissions versions make sure the four idle bypass screws are screwed in.
 

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Discussion Starter #7
Thank you DPeterson3 for your comment. Just in case I need to, how would I get in touch with Gordon Raymond?

Thank you Yvesmontreal for your thoughts. I will try plugging the hose to the brake servo and the tube off the #1 intake manifold barrel going to the camshaft cover and will see how that affects my readings.

Thank you Gubi for asking. I should have initially identified what type of Webers they are: I have a 1967 Giulia Sprint GT Veloce and the webers are 40 DCOE 27.

Mahalo (thank you) . . . 808Alfa
 

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Here's how. Part of Weber experience is NOT to adjust plates in a Weber unless you are good at it. The plates wear to match the bores with use and the bores develop slight plate grooves to match the plates. If that is disturbed, you are in trouble as the balance between throats in a single body differ.
Send me a PM with your e-mail address and I'll get back to you when I have a free moment.
 

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I recently had my Webers off for some head work and adjusted the throttle plates with a feeler gauge before installing. Will this provide an accurate measure of air flow between the two twin carbs. I am unable to get my Uni Syn in place for an air flow measurement. 2.0 liter spider with factory air box. What is the "best, low cost" method for synchronizing our twin Webers?
 

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Are you talking about in EACH Weber body, or between a front and rear Weber? Next, which specific Webers? Some have manometer fitting plugs which allow manometer measurements while early Italian Webers do not.
If you try to adjust air flow within a single body by moving plates around, you will likely cause plate binding in the throttle bore, resulting in eventual grooved throttle bores and / or worn plates. You will also lose the factory bar being centered in the body which will result in shaft end plate or balance link binding on the bearing pockets.
You can easily make a curved UniSyn adaptor of PVC that reaches around the corner of the inside of the cold air box to reach the Weber throat, if you do not have Webers with blanking plugs in manometer ports.
Finally, if each Weber had its plates set 100% closed before installation, or if plates / bores were worn, set so both throats in the same body showed close to the SAME amount of light leakage around the plates, the two Webers are easily balanced with the factory balance link.
A feeler gauge will NOT give you adequate balance in one body. Further, adjusting plates without a really good reason (bearing replacement, shaft replacement, or plate replacement) is not suggested. This is not a DIY job unless you thoroughly understand Weber design and assembly techniques, and have the tools to perform a factory set-up.
This is only my opinion from restoring Webers for many years. Below is a photo of the oldest set of 45DCOE9's I've ever seen, now with new bearings, bars and plates. Not a little job
1611215
1611216
1611217
 

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But Mad North-Northwest
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This is the tool I use with my SK synchrometer to sync DCOEs (p/n STE 6). As Gordon said you can probably Macgyver something up with PVC, but the rubber adapter isn't very expensive and works well.

 

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Tom,

Thanks, I will obtain this adapter and a new SK sync. Carbs are 40DCOE, "feeler gauge method" was used as a comparison between the two carbs, Not for adjusting individual throttle plates in one carb. My thinking was if the throttle plates are the same, the air flow will be the same.
 

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As a rule, at idle, few engines draw A/F in exactly the same way, so balance between Webers with good plate set-up is best done with some type of flow or manometer, or with just a little practice, by "feel" noting engine motion against mounts at idle. A/F idle needles can help a bit, again a practice learned by trial-and-error.
 

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I’m something of a contrarian on this.

I’ve found that manometers simply don’t have the degree of low-flow resolution to achieve the best synchronization.

having said that, your posts up to this point suggest you’ve either messed with the butterfly plates and/or there’s a bend or twist in your shafts or plates. Any attempts to tune-out such flaws are doomed.

as others have suggested, send them to Gordon for repair, and ask the guy who “rebuilt” them for a refund.
 

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I have not fooled with the butterfly plates. While the carbs were of I checked and compared the gaps between the plates and openings for information sake only. Following Tom's advice I have ordered the adapter and SK synchrometer for adjusting the airflow at idle
 

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My comment was based upon this...


I tried adjusting the "butterfly" plates on the carburetors thinking that was the problem but that didn't make any significant difference. ,
Plus, we don’t know what your rebuilder did. If he meddled with the plates, not good. Probably.

By the way, there’s nothing particularly wrong with removing the plenum to use your synchronizer. In my opinion, the only legitimate use of a synchronizer is to determine if the butterflies or shafts are wonked out of shape, or if there are some other flaws in the engine that will cause an airflow difference, ie:

vacuum leaks, wiped out cam lobe(s), leaky valves, etc.

Needless to say, broken engine stuff can’t be cured by carb adjustments.

Good luck!
 

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I agree with Don on manometers. I have owned several pairs of Webers over 20 years and I have tried various sync methods. I now remove the screw covers from over the progression holes and observe the position of the edge of the throttle plates with respect to the holes and adjust the synch screw to make them the same. It is simple, accurate and quick and it requires only a flat blade screwdriver and a flashlight
 

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I have gotten to where I don’t bother with the visual check described by Ed. As Gorden noted, “with practice” one can achieve a more perfect synchronization based upon behavior, rather trying to predict it with measurements.

for instance.... in addition to a perfectly smooth, and slow idle, when one suddenly lets off of the throttle to decelerate, you should hear that lovely sound of tearing silk. No pops or burbling. There is no observation or measurement that will get you there. It’s the tiniest of adjustments that will eventually meet this standard.
 

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This is quite true, and why I keep my special Weber screwdriver handy!
 
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