Technical Synchronize dual carburetors

I’m a bit confused on carb sync. I can’t seem to get them to work correctly together , can some explain the proper way of doing it ? Trying to syncc2 super sevens by speedway that are new , on my flathead ford v8 bored 60 over with 3/4 race cam and Navarro heads standard 3 3/4 crankshaft , iffy intake if any of that matters , bought a Holley unisync unit , but when I set to instructions and place it on top of either carb it smothers out the engine ?

 

You are starting out with the adjustable flow valve on the Unisyn fully open, right?

 

This was the best explanation I have found. So much so I keep a copy with my Uni-Syn. I found it on a previous post.





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Yes, open up the flow valve.

 

I've found using a Unison is iffy at best. It was never accurate the best I could tell. Use your ear! Listen to the pitch of the air rushing into the carbs and adjust the idle to get them in tune with each other. It's worked every time for me.

 

Be sure to remove your linkages from both carbs.
Adjust them to have even vacuum by moving each accelerator throttle separately. Then adjust the lengths of your throttle shafts to match your setting.

 

I use a dial indicator on the throttle lever to set each to the same opening. Doesn't matter how open or closed they are, as long as you set them the same, but, its better to be just off idle. Start engine, adjust each throttle stop a little at a time, turning each screw the same amount till the idle speed is right. If you have two indicators, all the better, but once you set them, you don't need to keep it in place as long as you turn each screw the same amount.

A tachometer is useful as well, you can see the rpm raise as you turn the screws, once it goes up, just back off till it comes back down even with the other carburetor. Just remember, use very small adjustments at a time.

My uni-sync doesn't work with my engine either, it just bogs it down. With a very low idle rpm ( 650 ) and dual carbs, not much air is flowing, so the uni-sync has to be almost closed before the ball ever rises.

 

I made an adapter from a carb cover and mounted a UniSyn to the top of it to do dual quads and Holley 2 barrels and could not be happier. A great tool in my cabinate.

 

You might want to check your Holley Unisyn. My last experience with one found that the unit was faulty. I could not get the bead to rise unless the Venturi was almost fully closed and it would choke out the engine. Fortunately I had a Uni-Syn that I picked up off of eBay that works fantastic.


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I use a aprox 1/4" id hose to hear air flow. I put one end into carb throat, .other end in ear & listen. I then do the same on 2nd carb. I put the hose in the same location in each carb, Adj throttle stops until sounds are equal. Greg

 

Unisyn tool is great, but as noted you will be chasing your tail unless the linkage between the carbs is disconnected. Can’t open one ****erfly without moving the other just compounds all your efforts. #3 post has the method down without complications.

 

I may be wrong on this, but I recall a bunch of threads regarding the poor quality of the new Speedway Super 7 carbs. I'm wondering if that may be the source of your tuning challenges.

 

I’ve been using an airflow synchronizer tool called a “snail” for years on my Porsches with Webers. It’s very sensitive and extremely easy to use. Works as well on my Strombergs. I also have a Unisyn but don’t use it.

 

Thanks for the input everyone

 

Let me throw a fly in your soup. I usually spit out the wings myself.

if you are running a common plenum as most V-8 intakes are you do not have to sinc the carbs. Just get them jetted right and opening correctly and run with it. You normally only sinc carbs when they are on separate plenums, like say a brace of one barrels on an inline engine. Some guys even get around that by running a cross over line between the runners.

 

****** is correct......but I like to have the same airflow going thru each carb and the mixtures all being close to the same.
Doesn't matter much but that's just me.

 

Had problems using a Uni-synch on my 97’s. Purchased a “Latest Range 000124“ and it works great on Stromberg 97, Holley 94 and SU carbs.

 

******'s wrong it's fly in the ointment, Not soup. However, he could be right on not bother with synching carbs with a common plenum. Just the same, I'll synchronize mine for the sake of having them pull equally. Here's a Youtube link from the VW guys. It helped me understand how to do it. Note he should have disconnected the linkage.

 

with separate plenums syncing is imperative with multiple carbs....totally different, but that's the tool I use.

 

I have 2 94's on an Offenhauser intake on my flathead and solid linkage so wanted the carbs set about the same. I disconnected the linkage and set the carbs where the suction felt about the same with the palm of my hand, did make a difference on how the car runs. Offenhauser recommends running solid linkage due to the placement of the carbs.

 

Could you use something like the synchronizer used for multi-carbs on motorcycles? I just saw a thing on FB that looks like you can set up to 4 carbs using vacuum ports to get a reading on the gauges.

 

Works for me, I usually check them every 2years.

 

Alanp561, That's exactly what I have to use on my O/T V-max. Even has little thumb air valves you can adjust to get the needles steady (no flutter). Lippy

 

Thanks, think it would work on a pair of 81's on a 59 AB?

 

No, this won't work on multiple carbs with a common plenum, because the vacuum signal to each will be the same. When balancing the carbs you're trying to ensure they're each drawing the same amount of air, you need something that measures the air flow in, like the Uni-Syn, not the manifold vacuum.

ETA, they work on a motorcycle because the carbs are mounted on individual runners, not a common plenum. Even so, they aren't measuring the air being drawn into the carbs, which would be the proper way to balance the carbs; but I guess it's close enough.

 

Piece of hose, one end held at right angle to your ear the other end held at right angle on carb top, you can minutely hear the difference.

 

Until I lost most of my hearing , that's what I did .

 

Jimmy,
Have you ever seen any change in your vacuum?
I’m just wondering. I’ve not noticed much of a change over the years with two flatheads.

 

Yeah, I should have thought of that. Thanks

 

IF , you had a pair of " hats" with adjustable openings And you had hose ******s in those hats that you could hook those MC balance gauges too , I'd think those gauges might work ?