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Can I use One Vacuum Gauge to sync my carbs?

10K views 15 replies 10 participants last post by  joshuarwp3 
#1 ·
Hello gentleman and thank you for your time,

I have a GL1200 and just rebuilt my carbs, I did do a bench sync following a youtube video but I would like to do a proper on bike sync as well, but since I live in Kuwait it is hard for me to shop online for the sync tools, I have two questions:

1- Attached is a vacuum gauge which I found in the flea market, it is just that one and an air hose attached to it, what is this gauge? is this a vacuum gauge? can I use this to get any reading from my carbs?

2- Is it possible to sync my carbs using just this ONE gauge? sort of like take an exact reading from one carb and attach the gauge to another carb and so on?
 

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#2 ·
It is possible but will be tedious to do it with one gauge. Someone on here did it by making a manifold with 4 aquarium valves. That gauge, unless you have it attached to a vacuum source, is seriously out of calibration. The needle should be resting at 0.
 
#3 ·
I wouldn't want to try to sync a 4 cylinder wing with a single gauge, at minimum you will want another. Especially since adjusting sync on one carb will affect the vacuum reading on the carb you are syncing it to (plus all others).

On the 1100's carb #3 is the base carb, all others sync to it. I suspect the 1200 has the same sync order.

First thing you'd want to do is get a reading on #3 and #1 carbs then swap the two gauges to compare readings (this checks the gauges themselves). On the 1100 you would sync #1 to #3, then #4 to #3, then #2 to #4, then re-check #4 to #3 and #1 to #3 settings. "Wash-rinse-repeat" if the #4 to #3 and #1 to #3 settings have changed, it might take a couple rounds to get them all lined up. Follow the sync sequence for the 1200 though, it may be similar but different.

With a single gauge that would be an awful lot of hose swapping, and you will still need at least two (and better to get 4) vacuum port nipples, and something to cap or otherwise plug a nipple that doesn't have a gauge connected.
 
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#4 ·
You can build a very simple manometer with just some clear vinyl tube and some fluid. Mercury works best in my opinion but heavy oil will work also. I use about 10 feet of tube for each manometer. It is cheap but the length doesn't matter as long as the tube is long enough. Put the liquid in both the tubes. Thow the tubes over a ladder or back of a chair. You need this so the engine can't suck the liquid in. Do this for both side. (left and right) Now connect one end of each tube to the carburetors. So on the right side one end to the front carb and the other end to the rear carb.Now go to the other side and do the same. The tube must hang in a way that it forms a "U" in the back of the ladders. Tape or fasten as needed to get the "U" shaped. While you are back there take a Sharpie and mark the height of the fluid at rest. Same for the other side. Now start the bike and run at desired RPM. Is the fluid still at the same Sharpie lines as when the bike was not running? If so you are done. If not adjust until the fluid returns to the original place. Right at the Sharpie lines. Now do the other side. Then set one tube aside and using the other put one end on either carb right and either carb left and adjust. All done.
Heavier liquids behave better. Light oils like ATF tend to splash around asome and can be difficult to make sense of. Mercury works slick. Gear oil is good. If you look at the attached image it will give you an idea. I like a ladder better as it is higher than the board and you really don't have to fasten it that firmly. Just a tape job works as well. You can see he has the engine running and that it needs a little tweaking. The oil should be level on both "U"s
 

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#11 ·
Syncing with one gauge is not something I'd rely on if I had 4 carbs, but each to his own!

I've got a 4 gauge set somewhere that I don't use anymore if you want it. Free. Shipping will apply of course.

But seeing as they all come from China, chances are it's cheaper, (given where you're at,) for you to get it direct.
 
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