Since I'm avoiding yard work, I'll do my best to explain the limitations of gauges and liquid column synchronization devices. I'm NOT saying that these devices don't work because they do work, but within their limitations. And their limitations are inherent in the physics by which they work. It's somewhat like using a 100 pound torque wrench to tighten something that should be measured in inch pounds. It will give you a ballpark but you can't get as accurate a measurement out of it. Out of balance carburetors and throttle bodies result in diminished horsepower, gas mileage, lean & hot running cylinders, as well as rich & cool running cylinders.
This first image is an oscilloscope voltage signal from the vacuum that is taken directly from a single carburetor port. Each sawtooth waveform portion comprises all four strokes of the engine.
In the picture below the part of the signal that is ramp upward is the intake stroke of the engine. The part of the signal that ramps down is the compression, power and exhaust stroke combined.
Inside the circle
on the left is the vacuum signal from the intake stroke and this is the only part of the vacuum that has to do with the synchronization of carburetors. The rest of the signal inside the circle
on the right is about the air intake system and its ability to breath and recover from the intake stroke and be ready for the next cycle.
Gauges, fluid manometers and their associated snubbers produce a fluttering indication that averages about the
red line in the picture below. It's not the true average of the vacuum signal as it's strongly influenced by the vacuum that remains after the intake stroke is completed.
The REAL
average vacuum signal developed by the intake stroke is shown by the
green line. But gauges and fluids have no way to deal with this reality.
Moving beyond mechanical bourdon gauges and fluid manometers is where modern technology comes in. Truly accurate carburetor and throttle body synchronization is best achieved by analyzing the vacuum waveform and identifying the min and max peaks of the vacuum that are created solely by the vacuum stroke of the piston. My sync gauge is software and hardware based so I call this technology a "digital peaking manometer". The entire vacuum signal from the intake stroke of the waveform is analyzed for synchronization as shown below. The rest of the signal is discarded for synchronization purposes.
Some final thoughts: If you want
peak performance from your engine you need to simultaneously synchronize your carburetors. Carburetor linkage has interplay between cylinders and unless you can see it all at once it can be a frustrating and drawn out process that ends up just being declared "good enough". Synchronization is best done with matched sensors and with matched, quality
hoses. Soft hoses diminish the vacuum signal getting to your gauge and mismatched hose lengths will distort the vacuum readings. So, you may get the readings the same but the actual running vacuum, as each cylinder sees it, may very well be out of balance.
