From: Flatheadmalc1 Sent: 2/11/2004 9:28 PM
Can anyone out there tell me how to use the uni syn device for carbs? I have my Dads old one but no instructions.

Thanks Mac

From: Bill Mumaw Sent: 2/12/2004 12:41 AM
Here is something I copied and saved about using the Uni-Syn from one of the forums:
With the engine at idle, you want to open the flow control as much as possible, but still keep the float in the sight glass at about mid-level. Then check the other carb, which wants to read the same flow rate. You may have to adjust the flow control a few times as you adjust the carb settings. Just remember to check each carb with the flow control set at the same point, and to keep the sight glass in the vertical to prevent the float from hanging up in the tube...

From: 29AV8 Sent: 2/12/2004 1:01 PM
I have 30 years of experience with UniSyn's, having owned lots of multi carb British things, including a V12 Jag with 4 carbs.

The wheel in the venturi controls the flow through the tube, or in other words how high the bead is in the cylinder for a given engine speed. You need enough flow to not strangle the engine, and the bead works just as well in the lower third (which still lets good air flow through). Make sure the idle speed doesn't drop when you place the tool on the carb: if it does, open it up.

Before setting the carbs, make sure that the ignition is right: points and timing set, good wires and plugs. Rich running is often blamed on carbs when in fact it's a weak, retarded spark. Check the throttle shafts: loose ones let in air and lean the mixture, raising idle speed, as well as throw off the linkage action. Check the linkage that connects the carbs: if it's loose, one will open before the other. Make sure there are no vacuum leaks.

If it's a twin carb set up, disconnect the linkage that connects one carb to the other. Set the idle speed with the linkage screws first. Use the UniSyn to check that each carb is drawing equally at idle. This may take a few tries until you get both drawing equally at the speed you want. Blip the throttle to see if they come back to those settings (worn throttle shafts can fool you). Set the idle mixture screws: I usually richen it until the idle slows down, then back it off. Check the balance again. Hook the linkage back up: if one carb now draws more, adjust the linkage until it's back to roughly equal.

Once the carbs are drawing equally at idle, have someone push the gas pedal and hold an engine speed: about 1500 rpm is fine. This checks that the mechanical linkage is pulling equally. You'll need to open up the center wheel to draw more air and bring the bead down in the tube. If both carbs are within a bead's thickness of each other, that's good. If one is definitely off from the other, the higher flow carb's linkage is being pulled more than the other. You'll need to figure out why that's happening mechanically to rectify it.

You can also compensate for loose linkage. If the front carb opens later than the rear, increase the idle setting on the front, reduce it on the rear. When the linkage is opened, the carbs can be in balance again. It's not great but it works.

With 3 carbs it's a little less precise. Disconnect the linkages, then set the idle on the center carb. Verify with the UniSyn that the end carbs are not drawing at idle. Seat the end carbs idle speed screws (if equipped) to where they just make contact without opening the butterflies.

Hook the linkage back up and set the engine speed at some point where all 3 carbs are at least partially open. With a progressive linkage you might find that the end carbs are pulling less than the center: that's ok as long as the end carbs are pulling equally. Adjust the length of the rod connecting the front to the rear to balance them.

The only way to know if all 3 are at wide open throttle is to visually check the butterflies with the engine off. The trick here is to accept that you don't have to have all 3 pulling the same amount at all rpm settings. The goal is that you are on one at idle and part throttle, that the end carbs are pulling the same, and that all 3 are wide open at full throttle. It's kind of an art setting the point where the end carbs begin opening, and kind of depends on how well your egine runs on one carb. I have mine set to begin to open the ends at about 1/3 throttle, allowing for cruising without running all 3 carbs.

Once the carbs are balanced, you can use other tools to determine mixture settings while the engine is running. A good smog test station can tell you what mixture ratio you're pulling. I have a little gas tester that goes up the tailpipe and measures carbon monoxide: you can determine ratios with the chart provided. 14:1 is best mileage, 12:1 is best power. The ideal is supposed to be 14.7:1, but it's hard to nail that figure. If I have all the carbs pulling equally and it's running about 13:1, that works pretty well. This analyzer has helped me find lean running conditions (works at idle or at part throttle) and runs about $200 from sports car places like Moss Motors.

Sporty car guys are one group that routinely plays with balance and mixtures, and they know it pretty well.

29AV8

 

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