Carb Synching

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John Vardanian
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Carb Synching

Post by John Vardanian »

Just curious as to how folks accomplish this task.

Does a uniform flow rate set at idle ensure a uniform rate of flow at higher rev?

john
PF Coupe
DWR46
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Re: Carb Synching

Post by DWR46 »

Beyond about 85% throttle opening, any carburetor is flowing the maximun amount of air, as the throttle shafts then restrict flow. So when the carbs are wide open, they are in effect synchronized as long as they have the same size choke tubes installed.

Setting the synchronization at idle is most effective because at that speed the carb is flowing the least amount of air and changes in air flow are most easily quantifiable on a uni-syn tool (in effect, the tool is most sensitive to air flow changes at low engine speeds).

Even using the tool at higher speeds would only work if you were running the engine on a dyno where you could "load" the motor, as higher revs with no load actually does not open the carb butterflies very much.
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TOMKIZER
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Re: Carb Synching

Post by TOMKIZER »

Don't forget left to right synchronization. The best thing I have done to improve my carburetor behavior was to start from scratch and reset the plates by resetting the toothed sectors and closing all the air bypass screws. That allowed me to use the air bypass screws to synchronize the left and right bores of each carburetor to each other before synchronizing each carburetor to the others. Unless that is done, only one bore of each carburetor is really synchronized, leaving half the cylinders effectively unsynchronized. My car is running better than ever, at all speeds, and starts instantly, even when cold.
Tom Kizer
So many sidewalk cafés - so little time left.
1969 365 GT 2+2 S/N 12293 (Gone but not forgotten)
1967 230 SL 4-spd (Currently on CPR)
John Vardanian
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Re: Carb Synching

Post by John Vardanian »

Tom K, how do you disengage one throttle shaft from the other?

A question for Dyke, how about using vacuum gauge at each throat as opposed to the conventional unison suction meter?

Thanks.

john
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DWR46
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Re: Carb Synching

Post by DWR46 »

John:

You really want to measure air flow, not vacuum. Now, I certainly have used a Vacuum Gauge to set the idle mixtures, as the gauge will show very small idle speed increases, but I would question a Vacuum Gauge's suitability for actaully synchronizing air flow through carburetors.

A comment on using the Air Bypass Screws on those carbs so equipped. Always start with ALL the Bypass Screwas closed. Synchronize the highest air flow barrel of each carb together, using the idle speed screws, and then use the Bypass screw to raise the lower barrel of each carb to march the already set barrels.
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TOMKIZER
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Re: Carb Synching

Post by TOMKIZER »

John,

I agree with Dyke. Although the error created by synchronizing left to right first is perhaps negligible, it is theoretically greater than synchronizing the high-flow venturi first. It seemed to me that the air flow sensitivity was greater when changing the idle speed screws than the changing the bypass screws. So syncronizing first with the idle speed screws is a good idea. The low-flow venturii can be brought up to equal the other without messing with the idle speed screws.

Regarding your question, I'm completing a procedure that I started some time ago. It explains just how to set up a carburetor from scratch in preparation for synchronizing and setting idle mixture on the engine. It includes the sector gear set-up. I'll email you a copy when I'm finished.

Tom Kizer
So many sidewalk cafés - so little time left.
1969 365 GT 2+2 S/N 12293 (Gone but not forgotten)
1967 230 SL 4-spd (Currently on CPR)
Timo
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Re: Carb Synching

Post by Timo »

John Vardanian wrote:Just curious as to how folks accomplish this task.

Does a uniform flow rate set at idle ensure a uniform rate of flow at higher rev?

john
Trying to put it simply and in general terms:
First, set uniform idle air flow on each throttle bore of each carburetor using "air flow meter" (i.e Uni-syn, STE Synchrometer or ...?). To obtain appropriate and smooth idle, you usually have to also adjust/set the mixtures of each throttle bore.
And don't forget to check/adjust dwell and ignition timing, while at it.
Secondly, to ensure closest uniform flow rate at higher rpm, adjust carburetor-to-carburetor throttle linkage to closest possible, simultaneous throttle valve operation (="synchronized" opening) on each carburetor.
Timo
John Vardanian
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Re: Carb Synching

Post by John Vardanian »

Thanks Dyke, Timmo, does the 36DCL have an air bypass screw, if so which one is it? Thanks.

john

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250GT
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Re: Carb Synching

Post by 250GT »

John Vardanian wrote:Thanks Dyke, Timmo, does the 36DCL have an air bypass screw, if so which one is it? Thanks.

john

Image

John, I cannot find the idle speed screw either !
Must be an horizontal adjust screw with spring normally can be turned by hand.
Cornelis.
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Horizontal screw are idle screws on both sides 40DCL-6 Webers
Horizontal screw are idle screws on both sides 40DCL-6 Webers
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250GT
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Re: Carb Synching

Post by 250GT »

Synchronising is always a bit frustrating after 200 km it has change again a little bit,
I drive with open trumpets so easy to check: be happy with an airfilterbox.
If you would have it perfect, you must buy a fuelinjection car.
but REAL perfection is boring .
ciao
Cornelis
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TOMKIZER
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Re: Carb Synching

Post by TOMKIZER »

I think maybe there isn't one on your carburetor. Here's a photo of the one on my Queen (40DFI/5). There is an identical one on the other bore.

Is a PF carb the same as a GTE carb? If so, I think maybe the left-to-right plate synchronization has to be done with the little cone shaped tube and the lock clamp on the primary throttle shaft.

Tom Kizer
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Air Bypass Screw.jpg
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So many sidewalk cafés - so little time left.
1969 365 GT 2+2 S/N 12293 (Gone but not forgotten)
1967 230 SL 4-spd (Currently on CPR)
DWR46
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Re: Carb Synching

Post by DWR46 »

Come on you guys, you all are supposed to be the experts out there, but I will take a shot at which carbs have Bypass Screws. The first Ferrari to have Bypass Screws was the 40 DFI2 equipped 330 GTC. I believe all DFI's, later DCN's (Daytona), Later DCNF's (Dino) and all the Boxer carbs have Bypass Screws, but no DCF,DCL,DCZ.

Many years ago, I wrote a two or three part series of articles for the Ferrari Market Letter on how to set up carbs and the linkage on the various cars. They were also published in the Tech Tips Book that I did with Jim Riff. I believe they are still the correct way to do the carbs. The articles cover how to synch the separate barrels, set the sector gears, adjust idle mixtures and set up the linkage for even throttle opening.
250GT
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Re: Carb Synching

Post by 250GT »

DWR46 wrote:Come on you guys, you all are supposed to be the experts out there, but I will take a shot at which carbs have Bypass Screws. The first Ferrari to have Bypass Screws was the 40 DFI2 equipped 330 GTC. I believe all DFI's, later DCN's (Daytona), Later DCNF's (Dino) and all the Boxer carbs have Bypass Screws, but no DCF,DCL,DCZ.

Many years ago, I wrote a two or three part series of articles for the Ferrari Market Letter on how to set up carbs and the linkage on the various cars. They were also published in the Tech Tips Book that I did with Jim Riff. I believe they are still the correct way to do the carbs. The articles cover how to synch the separate barrels, set the sector gears, adjust idle mixtures and set up the linkage for even throttle opening.
Right,
Till 1964-65 the 36DCS(Lusso +SWB) Im never find them.
My F- knowledge dont get futher...........sorry.
36-40 DCL and DCL are technically spoken from the same famely identical except the material .

C.
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Re: Carb Synching

Post by 8339 »

I hate to jump in but here goes:

John,
-First without making sure the ignition is up to snuff the rest is waste of time; dwell and timing are crucial
-The throttle linkage needs to dis-connected from the carbs so they all independant from each other
-Before starting the engine check to see if the throttle shafts have any kind of play, if it's excessive you'll always have a vacuum leak and what ever settings you make will change constantly.
-On the DCLs and DCZs there are four adjustments. On the right side is a throttle stop adjustment which actuates the right side gear of the throttle shafts. On the opposite side (left side) is the throttle openning adjustment which is used to synchronize each carburetor. Tom Kizer mentioned making sure both throttle plates are fully closed and the gears are timed correctly. For the most part I've not seen these get out of adjustment unless someone else has been in there. The other adjustment is the idle mixture screws one for each throat.
-With all the linkage dis-connected use a Synchrometer, Unisyn, start the engine, you may have to adjust a throttle stop with one carb to keep it running. With the engine reasonably warm adjust the throttle opeening to match all three carbs. Side to side should be the same or close due to the gearing. If you don't have Synchrometer the old method is to use a vacuum hose and listen to the volume of air. There are times when I still use this method and it works.
-adjust the idle mixture, screw it in until the RPM drops and back it out slightly, use a hand held tach and watch it. Small adjustments 1/8 of a turn and let it settle. If you need a starting point usually 2 1/2 turns out from bottom works well.
-Once it appears to be even match up ther linkage so that none of the adjustments change.
-I have no way to quantify this but I would bet that a great majority of these carbs have worn out throttle shafts making that much more difficult to set up properly.

Sorry for diatribe and I hope it helps. If I've missed something let me know!

Richard Garre
Radcliffe Motorcar Company.
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TOMKIZER
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Re: Carb Synching

Post by TOMKIZER »

DWR46 wrote:Many years ago, I wrote a two or three part series of articles for the Ferrari Market Letter on how to set up carbs and the linkage on the various cars. They were also published in the Tech Tips Book that I did with Jim Riff. I believe they are still the correct way to do the carbs. The articles cover how to synch the separate barrels, set the sector gears, adjust idle mixtures and set up the linkage for even throttle opening.
Dyke, I've got the third edition of Ferrari Tuning Tips and Maintenance Techniques, the one by Apen and Roush in 1975. They apparently took out the parts about syncronizing the separate barrels and setting the sector gears in that edition. They refer to a tech tip by Fred Leydorf in Prancing Horse #29 and corrections in #30, which I don't have.

I've got John Passini's Weber Carburetor book, the Haynes Weber Carb book, Apen and Roush's third edition, the 330GT 2+2 service manual, some 40DFI-2, 5, and 6 sheets from the Weber Catalogo Generale, and some stuff from Allen Bishop. Little of it goes into enough detail about syncronizing left-to-right and setting sector gears. Since most of these books and articles are no longer in print, often since many years, it would be wonderful if someone could "legally" make downloads of them available to those few remaining vintage Ferrari owners who are willing and "not afraid" to use them. Do you have any idea where they might be had for a reasonable price - like the original articles you did or the early version of the Tech Tips book?

Richard, after 41 years, my sector gears had developed enough wear that I had to resynchronize the plates. The driven shaft was more closed than the driving shaft because of the sector gear wear. It took a little magic to get them right. Bias the driving shaft one way with one finger of the left hand, bias the driving sector gear the other way with another finger to take up the gear slop, hold the driven plate closed with your the right hand and tighten the lock nuts with your third hand and a wrench. And when it doesn't work just right, start over.

Isn't this fun?

Tom Kizer
So many sidewalk cafés - so little time left.
1969 365 GT 2+2 S/N 12293 (Gone but not forgotten)
1967 230 SL 4-spd (Currently on CPR)
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