The Stovebolt Site Forums The Shop Area Engine Shop dual carb set up?

I have been thinking about getting a dual manifold and puting dual
carbs on my 1952 Chevy. But, I have heard horror stories that tuning
dual carbs are nothing but a pain in the butt. Yet, I see alot of dual
carb set ups in the pics. Is there a meter I can use to set the carbs
correctly if I go that way? If not, what is the secret to tuninig dual
carbs? Is the gas milage better with dual carbs opposed to the single
carb.?
John

there is a gauge, look in speedway or jegs, i think is called a carbsync.. the milage will be less, you are pouring gas thru two openings instead of one. i got 15.4mpg last week mixed driving. i have dual carbs dual exhaust and a 5 speed s-10 trans and 15 inch tires. i have gotten as high as 19.2 averaged over two fillups but i think one carb was not working. mho. ron

Yep a unisync and a tach. is all you need.

People tend to shy away from twin carb set-ups because they seem complicated.These are relatively simple one barrel carbs.
The most common mistake is they try to balance the carbs by adjusting the linkage.WRONG!
As Ron,Toyvo and Curt have said get a Unisync. Get both carbs set correctly then adjust the linkage to open both carbs at the same time.
I did this for years on my VW Bug (twin,two barrel Dellorto carbs) and ironically got better gas mileage on account of them being correctly jetted and more fuel efficient,as long as I didn't thrash it!

I balanced my dual Holly Webers by using a Dwyer magnehelic gauge and some rubber tubing. Set up the gauge and then inserted the tubing (with a pitot tube attached) in the throat of each carb. Then just adjusted each carb to that the DP pressure readings were the same. Also need to make sure that the dual carb linkage is dead on and open each carb equally and at the same moment.

As stated above, the Uni-Syn carb is an excellent way to balance the carbs (I used them on VWS, Porches, and British sports cars back in the 60s & 70's). You might need to make an adapter tube to make a good seal to the top of the carbs, depending on what carbs you use. I have used short pieces of plastic pipe with a rubber gasket on the carb side of the pipe. The Uni-Syn has a rubber seal on the bottom and should seal on the top of the plastic pipe. If you make two pipes, you can easily move the Uni-Syn from pipe to pipe (carb to carb).


If you want an adequate, back-yard adjustment, it is also possible to balance the carbs with a vacuum gauge (with or without a tachometer).

1. Set the idle speed you want by adjusting one of carbs until you observe (on a tach, or, by ear) an increase (or decrease) in rpm. You can raise or lower the idle speed by going back and forth between carbs and increasing or decreasing each carb until you "balance" at the speed you want).

2. Adjust each carb's mixture to maximum vacuum after adjusting the idle speed to match on both carbs (if you have access to the mixture adjustment). This works fine with one and two-barrel carbs on the the old sixes.

3. If the idle speed is too high or two low after adjusting the mixture, go back to step one.

I've done this with stock Rochesters and with two-barrel Carter-Webers and it closely matches the Uni-Syn setting.

Install one at a time on a stock intake and get each carburetor running as best as you can. Then when you go to two, half the work is all ready done. The jetting will be very close with one or two. The engineers design the carb to use X amount of fuel with X amount of air for a optimal air to fuel ratio. The carb determines this ratio so it doesn't matter what engine its on or how many you use. Set the throttle openings with a Uni-sinc then adjust the linkage just as stated above. The most you have to adjust is the idle mixtures and maybe the choke. Joe

Thanks for all of the helpful insights guys! Looks like next year I will have twin carbs after reading all of this positive information!