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Comment by taborj | Hacker News Reader

Syncing carbs is an art. This is pretty interest to see how to inject a bit of science into it.

When syncing the dual SU carbs on my MG, the "traditional" way is to take a length of tube, remove the air cleaners, fire up the engine, then stick the tube inside the end of the carb. Take the other end and put it near your ear; you'll hear the airflow. Now stick the tube into the other carb. If it sounds the same, you're pretty close. Turns out the ear is pretty sensitive to detecting the changes.

I also have a "bubble-type" or "SU type" tool[0] that you put over the ends, and the vacuum moves a little ball in a tube.

[0] Similar to this: https://www.jbugs.com/product/5746.html

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backfire and you'll go deaf!

There's also the rods some people use, stick them in the top where the dashpot covers belong and watch how they go up and down.

I use the speed-up -> stumble technique and you don't need the tool for the fast idle, I just look into the throats of the carbs to see if the pistons rise and fall together.

https://youtu.be/4nvGLgO6pj0

I did the same on my MG. Buddy of mine used to so it on his Jaguar V-12 XKE with Zenith-Stromberg carbs...took a couple of hours to get it right. :-)

Those Jag V12s are so cool, though. Carbs as far as the eye can see....

I have a vacuum gauge I used to tune the twin SU's on my 72 MGB. It combines art and science. Worked on my 440 sixpack as well.

Oh, that’s VERY interesting. I never thought about ‘hearing’ the vacuum in the intake.

It's kinda wild. You can hear the different pitch in each carb.

> Syncing carbs is an art.

I fail to see how it's an art at all.

This is perfectly and trivially measurable, it's rudimentary science.

You can construct a manometer from a U of clear vinyl tubing with some water inside, affix one per throttle. If there isn't an existing vacuum port per throttle provided for this purpose, you improvise extensions on the inlets for your hose barbs to tap into.

At that point you just adjust things until the water levels are even.

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