How to Sync Dual CarburetorsBY MICHELLE SCHAEFER car engine image by itsallgood from Fotolia.com The procedure of synchronizing carburetors is relatively easy once the basic principle behind it is understood. In a dual-carburetor engine, both carburetors must be set to the same idle specifications and must open at the same rate. If one carburetor opens faster than the other, the engine may experience poor power or hesitation. The process of synchronization is a mechanical process that ensures not only that both carburetors open at the same rate, but also that they produce equal power. Step 1Remove the air cleaner or air cleaners and set them aside. Start the engine and bring it to normal operating temperature. Check for vacuum leaks at the carburetors by spraying starting fluid around the base of the carburetors. A change in engine operation or idle speed when you spray the fluid indicates a vacuum leak. Repair any vacuum leaks before proceeding with carburetor synchronization. A vacuum leak will make it almost impossible to properly synchronize the carburetors. Step 2Turn off the engine and disconnect the carburetor linkage from both carburetors. Most dual-carburetor engines use a 1/2-inch nut on a ball joint to attach the linkage to the carburetor throttle bar. Place the Dvorak Multiple Carburetor Synchronizer on the air inlet of one of the carburetors. Ensure the synchronizer float glass is vertical and the float ball is free to move. Restart the engine and allow it to idle. Turn the air adjustment screw of the synchronizer so that the float ball is centered exactly halfway up the glass. Step 3Move the synchronizer to the other carburetor and place it on the air inlet. Adjust the carburetor until the float ball is in the exact same position as on the first carburetor by turning the carburetor throttle stop set-screw clockwise to increase the vacuum reading or counterclockwise to decrease the vacuum reading. Move the synchronizer back and forth between the two carburetors and adjust each one until the float ball reading is exactly the same on each. Step 4Lower the idle speed of the engine by reducing the higher of the two carburetors to match the lower one. Increase the idle speed of the engine by increasing the lower-reading carburetor to match the higher-reading one. If the idle speed is correct but the carburetor synchronizer float readings do not match, turn one carburetor adjusting screw clockwise while turning the other carburetor's adjusting screw counterclockwise by the same amount. Step 5Reconnect the throttle linkage with the engine still running. Loosen the lock-nuts on the ball joints of the throttle linkage. Turn the connecting rod in or out until the ball joint end fits into each carburetor's throttle lever without binding or changing the idle speed. Adjust both ends of the linkage and tighten down the throttle linkage lock nuts and throttle-to-carburetor linkage nuts. The throttle linkage must have a no-resistance slip-fit onto the carburetor throttle arms. Retest the carburetors with the synchronizer. There should be no change in the readings after installing the linkage. Step 6Adjust the idle mixture by turning the idle mixture screws all the way in until they gently seat. Turn the screws counterclockwise three to four turns. Turn each screw clockwise an equal amount on each carburetor and note the engine idle speed. It is important that the mixture screw on each carburetor be turned an equal amount. Continue turning the screws clockwise about 1/4 turn at a time until a stumble in the idle is noticed. Back each screw out counterclockwise 1/4 turn to set the final adjustment. Open and close the throttle to observe the linkage for symmetry of operation and for binding. Adjust the linkage by adding shims or by bending the rod if required. Observe the linkage at full and part-throttle openings to ensure equal operation of the throttle plates. itstillruns.com On Jan 3, 2022, at 4:59 AM, derrickb81@xxxxxxxxxxx wrote:
Hi Bill,
I made one up yesterday from a 4” PVC cap. The ID to fir the 3447 is just 4.25”. Since the cap was just a bit larger, I used a strip thick walled vinyl tape around its inside perimeter to take up the little bit of slack. Now just waiting for my vacuum gauge to arrive. Sent from my iPad Derrickb81@xxxxxxxxxxx On Jan 2, 2022, at 10:36 PM, Bill Parker <hemirr@xxxxxxxxx> wrote:
The original poster says he has 3447 carbs, which have the smaller AFB air horn compared to the 3705 and any newer AFB, all AVS, and all Edelbrock. Just looking at Jegs etc I didn't see any to fit the smaller air horn, which is what I would need too. I'm considering getting one of these put together based on the great info provided in this thread, but unless someone has a source for a hat for 3447, one would have to add a big-to-small adapter under the hat, under the synchro assembly. Oh well I probably have one stashed somewhere. Bill & Kathi Parker, South Central Indiana You can buy a cheap carb bonnet and Edelbrock synchronizer and mate them together easily to work. You have to disconnect the carb linkage and only adjust the idles to match vacuums one at a time. It works miracles!
Here that video from Shepherds Garage
Yes it really works well. Great tuning tool David! Originally made by Edelbrock as well but without the carb hat…I believe I have one of the original Edelbrock “Uni-Syn” carb synchronizers in my parts stash somewhere. ![]()
Gary P. I use the Dvorak 4 barrel carb synchronizer on my 1962 Dodge Polara 500 Crossram. They take the single carb motorcycle synchronizer and attach it to a housing that fits over a 4 barrel. Click on this link: https://www.dvorakmachine.com/ I got mine from Dvorak 6 years ago for $99. Without synchronizing the Crossram carbs the engine will not run properly. If I can find the old video on YouTube of how to use it I will provide that too. --
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1962 to 1965 Mopar Clubhouse Discussion Guidelines:
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Please address private email -- email of interest to only one person -- directly to that person. That is, email your parts/car transactions and negotiations, as well as other personal messages, only to the intended recipient. Do not just press "reply" and send your email to everyone using the general '62-'65 Clubhouse public email address. This practice will protect your privacy, reduce the total volume of mail and fine-tune the content signal to Mopar topic. Thanks!
1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html.
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Please address private email -- email of interest to only one person -- directly to that person. That is, email your parts/car transactions and negotiations, as well as other personal messages, only to the intended recipient. Do not just press "reply" and send your email to everyone using the general '62-'65 Clubhouse public email address. This practice will protect your privacy, reduce the total volume of mail and fine-tune the content signal to Mopar topic. Thanks!
1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html.
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Please address private email -- email of interest to only one person -- directly to that person. That is, email your parts/car transactions and negotiations, as well as other personal messages, only to the intended recipient. Do not just press "reply" and send your email to everyone using the general '62-'65 Clubhouse public email address. This practice will protect your privacy, reduce the total volume of mail and fine-tune the content signal to Mopar topic. Thanks!
1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html.
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Please address private email -- email of interest to only one person -- directly to that person. That is, email your parts/car transactions and negotiations, as well as other personal messages, only to the intended recipient. Do not just press "reply" and send your email to everyone using the general '62-'65 Clubhouse public email address. This practice will protect your privacy, reduce the total volume of mail and fine-tune the content signal to Mopar topic. Thanks!
1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html.
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Please address private email -- email of interest to only one person -- directly to that person. That is, email your parts/car transactions and negotiations, as well as other personal messages, only to the intended recipient. Do not just press "reply" and send your email to everyone using the general '62-'65 Clubhouse public email address. This practice will protect your privacy, reduce the total volume of mail and fine-tune the content signal to Mopar topic. Thanks!
1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html.
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Please address private email -- email of interest to only one person -- directly to that person. That is, email your parts/car transactions and negotiations, as well as other personal messages, only to the intended recipient. Do not just press "reply" and send your email to everyone using the general '62-'65 Clubhouse public email address. This practice will protect your privacy, reduce the total volume of mail and fine-tune the content signal to Mopar topic. Thanks!
1962 to 1965 Mopar Clubhouse Discussion Guidelines:
http://www.1962to1965mopar.ornocar.org/mletiq.html and http://www.1962to1965mopar.ornocar.com/general_disclaimer.html.
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