It measures/compares air flow, period. So it can be used to make both carbs draw the same air flow, at idle, mid range or full throttle....if you have the linkage skills.
Yep, used to use mine to balance the twin SU's on my 66 Volvo wagon (long gone). Dead simple to use in that application.
Austin healey, Volvo, Triumph, Datsun, motorcycles, my dual carbed Mopar flathead, You scope the air flow indicated by the little puck that moves up and down in the tube. Matching the position at different rpms, allows you to adjust the linkage to assure the carbs are flowing the same air. So if your running triples with progressive linkage you ca make sure the secondaries open at the same rate and time as eaxh other. If you running dual 2bbl or singles, with non progressive linkage the same deal so all cylinders are getting the same mixture. So not adjusting the carbs but synchronizing the linkage.
Mandatory for SU's and Weber's if you want your car to run exceptionally well especially if you're running on independent runners.
On most british SU carb setups the carbs sit side by side and the linkage between the carbs can be adjusted independant so not to change the other carb. The Uni-syn helps balance the airflow after you set the fuel metering so they are equal.
That's a big YES, I think i could use one in my sleep. If we knew what you are tuning it would be a big help. IE, Intake type, Type of carbs, linkage etc
An excellent and simple tool. Simple design and simple to use. One correction of some of the above replies. A Unisyn is used to balance carbs with the interconnecting linkage disconnected. After the carbs are properly balanced then the linkage is installed and it's adjusted so as to not affect the balance.
To add to your correction; After the idle synch is done with links off, then the links are re-attached to maintain same idle flow, and then the high speed synch is checked/reset.
F&J, I am curious as to the function of a Unisyn at other than idle. I have only used them at idle. Adjusting idle speed and mixture. Going back and forth until both were perfectly matched with the linakges disconnected. At higher RPM there is not enough airflow with a Unisyn in place. It would literally choke the engine and result in a rich mixture....if the engine could continue running. On Alfa and Ferraris (the real ones...V-12s) you could also short pairs of plugs on individual cylinders and listen to the changes. This would get you real close. Granted, it has been quite some years since I used one, but I was Unisyn-friendly for about forty years. Please help my memory banks recover.
The Uni-syn I used was also for Webers/SU's or small inlet carbs only, as it must cover the inlet or throat completely, so it will not work on a Holley or an Edlebrock "large mouth" carbs. You never mentioned what carbs you have. I've had mine since the 60's as well. Got it from my neighbor as a gift for helping him with his MG TD when I was 15.
I believe you can still buy them new in JC Whitney. I know its the same concept, but seems like simultaneous vacuum gauges would be more precise.
My Uni-Syn is straight out of the 60's - my dad bought it to tune his 356 back in the day and was passed on to me in the mid-80's when I got my first British car . I've used it literally hundreds of times (I work on/restore old British tin) . It's a great tool if you know how to use it . Works on multi-carb motorcycles too .
I used one for years tuning Norton's, Triumphs and BSAs. Very handy tool for the right application. I think the other guys explained how to use one well.
My first and only "factory training" on setting duals, was in March, 1970 in Orangeburg, NY at the VW training school. They had a 66 VW type 3 pancake motor with factory dual Solex 32's. First step was idle flow, links off. High speed; there was a factory tool that hooked to the main accelerator bellcrank that allowed it to be adjusted for 1800 rpms, as I recall. Then open the thumbwheel adjuster on the Uni-Syn all the way open. Then place it on the carb and keep closing it until the float gets to the mid scale. The tearcher was a smart ass He'd break up the class in 2 member teams, then send us out in the hall while he "messed up" the carb adjustments, and then have us try to sort it out. The last team; he never messed with the carbs, he only swapped the coil wire from the center of the cap with one plug terminal. Yes the car started and ran...like crap...and the team tried in vain to fix the carbs
I don't like the Unisyn that I bought way back in the early 70s. I never could get it to work for me. (operator error probably) I bought a Holley syncronizer and never looked back. It's still in the tool box. I learned on Man-a-fre so it was a real PITA compared to 2 deuces. When I bought my 34 P/U it ran just fine and idled well. Just for shits and giggles I checked the carbs and almost all the idling was coming through the back carb and almost nothing through the front carb. The imbalance stays the same all the way through to WOT so one of them never got to WOT. A little bit of adjusting and they are now balanced. Did it make a huge difference?...no but I know that all the cylinders are getting equal fuel and air. I did a tech post on synchronizing dual 97s many years ago now using the Holley when I did my truck. It's probably still here someplace if you want to do a search.
you can get one from just about any vw performance shop. another model "the snail" is supposed to work better, but ive never used it.
I never had a unisyn, but Dad had a board with three home made U tube namometers attached. One for each carb on the 6cy stovebolt. You could see all three at once as they were side by side. It sure made the job easy.
part of my job interview was to identify one of these tools.it had 6 vacum line ports,6 glass tubes with balls and 6 knobs. was a unisync,but for what i didnt know.they were satisfied i knew what it was and how to use one,but this particular model was for a 6 cylinder outboard motor-mercury factory tool.very nice-made of brass. i have only used them on snowmobile engines.
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