The Stovebolt Site Forums The Shop Area Engine Shop Dual Carb Sync Tool?

Has anyone used one of the dual carb
sync tools from LMC Truck? I have a
Fenton dual carb setup with single bbl
Rochesters on my 1955 Chevy 235 that
was bored .060 that needs some tweaking.

Can you provide a link to that tool, and/or a part number?

If you are referring to a UniSyn,yes they work well provided there are no vacuum leaks in your intake/exhaust system and your carbs are matched and balanced as to jetting.


http://www.pegasusautoracing.com/productdetails.asp?RecID=826

If you're talkin about P/N: 38-1260, the Uni Syn, they SUCK!! At least I think so.

I used to have an engine in my car that ran dual Weber 40 IDF carbs. Basicly one individualy tunable barrel per cylender, and that particular item about made me want to blow up my car,...

Of course what Drew said is the 1st step, assuming you havea tight system and a set of matched carbs, the Uni-Syn can work, ok-ish.

STE synchronizers are better by vast amounts, and of course like many tools, you pay a bit more for "better".
They are very easy to use and dont require and fiddling around with adjustments on the tool at all. Take it out of your tool box, pop it on the carb, and take your reading.
I bought one long ago and still use it today, this thing is the poo for setting up multiple carbs. I highly recommend them.

I used a unisyn on my truck, and didn't really like it.

I switched from B's to W-1's a year ago, and of course, the truck will idle with the throttles closed, so I sync'ed them mechanically on the bench, and then just used a piece of windshield washer hose to set the idle mixture.
After this, I just payed attention to the spark plugs, and made small adjustments accordingly.

ChevyTruckKy,

What tool are you referring to?

"Rochesters on my 1955 Chevy 235"

What year Rochesters?

Do they have an air cleaner bolt in the top or does the air cleaner clamp around the top?

I have successfully used a UniSyn tool on both styles of Rochesters. But, I was just as successful performing a "manual tune" using a vacuum gauge and and/or a tachometer.

The tools in question are mainly for setting idle speed, they do nothing for mixture. The come in handy for setting throttle linkage.

Try unhooking the throttle linkage and set the idle on carb as close as you can. The slower the idle speed, the easier it is to hear a difference. A vacuum gauge might help at this point. Setting the mixture screws is just a matter of bottoming both out, then backing out equal number of turns on each one. Just remember if you turn one, turn the other as well. They have to stay together.

Joe

Using a vacuum gauge, adjusting for maximum vacuum, is a mixture adjustment.

Tim thats what I meant to say, I just did a poor job of doing it. The vacuum gauge works very well for setting mixture screws. Just take your time and do each one three or four times or till you know each one is as close as you can get.

Once you have driven around for awhile, its a good idea to check again once everything has had good heat cycle.

Joe

idle with the throttles closed

Well, they never completely close.

The idle mixture screws will only be the same number of turns if the carburetors are exactly alike (including throttle shaft leakage, float level). Better to get each one to idle best separately, then use the Uni (or whatever) to set the idle speeds to match.
The speed matching above idle is done with the linkage; the arms must be the same length (throttle shaft to link hole), and be at the same angle with no slack.
Yes, you have to go back and do the mixture again if the speed changes by more than a little.
Important: if the ignition isn't correctly set, you're wasting your time - this must be done first.

Lots of great advise listed here on this tricky subject. I thought the Unisyn would solve my dual carb probs too, but as mentioned above, your linkage must be in perfect condition, work smoothly. And your throttle plates MUST open exactly together, not one leading the other. I screwed with the Unisyn for some time without much success, until a friend came by and had the thing working perfectly in about 5 minutes without the Unisyn.

I am somewhat surprised at the number of negative comments concerning the Uni-syn on this thread.

Possibly this stems from a misunderstanding (or a previous misunderstanding) of the use of the tool.

The Uni-syn is a tool that will aid in the synchronization of LINKAGE on a multiple carburetor setup running solid linkage.

It will NOT Help:

(A) progressive linkage setups
(B) mismatched carburetors
(C) carburetors of the wrong size
(D) carburetors which are improperly rebuilt
(E) mixture calibration

I started working on multiple carb setups in about 1960. At that time, the Uni-syn was a tool of the wealthy. I learned to synchronize carburetors using a piece of vacuum hose. When I could finally afford a Uni-syn, I was in "hog heaven"

I still have the first Uni-syn I purchased, about 1966, and yes it still works well. And it has been used on everything from 2 to 6 carburetor setups...............successfully.

Jon.

Not only do they work, it look impressive when people are standing around watching!

Joe