How to synch your carbs

When "synching" carbs, what you are trying do is synchronize the throttle plates of the 4 of them. Ideally, each cylinder is carrying 25% of the load. Carbs that are not properly synched will affect the quality of the idle. It's a good idea to check the valve clearance before checking the carb synchronization, as it can affect the synch adjustment.

That rubber cap is where you will be connecting the rubber lines from the manometer (the synch tool). You do have one of those, dont you?
The most common are the mercury tube type. They're inexpensive and will get the job done. Another common type consists of dial gauges in a rack. The best kind of all is one that you can borrow from someone for free!
Don't lose those caps. You'll be putting them back on when you're finished.

Now, we're almost ready to get started. If at all possible, it's a good idea to have a house fan in front of the engine to provide cooling air. If you're doing this for the first time, it might take a while and that air and oil cooled motor can get very warm in a short period of time. You'll also need a phillips head screwdriver to make any necessary adjustments.

Go ahead and pull the gas tank. You'll need something to use for a temporary tank while you're doing the check/adjustment. I use a plastic bottle with a cone shaped cap. I connect a piece of fuel line to a plastic T-fitting which, in turn, is connected to the 2 fuel lines that you disconnected to remove the tank. You can get some very nice devices that are sold for just this purpose*. If you don't mind spending a little extra cash, go for it.

Connect 1 hose from the manometer to each of those 4 fittings. Keep track of which hose goes to which fitting or you'll be chasing your tail when it comes time to make adjustments. (You've been warned.)
Also, be sure to block off the vacuum line to the petcock. A vacuum leak like that will cause you problems.

Now, fire it up, let the motor warm up, and set the idle to approximately 1700 RPM by the tach. Here's where the idle stop adjuster is located. Turn it clockwise to increase the idle. You shouldn't have to turn it very far.

If you're using the mercury type manometer, be careful with the throttle. If you rev the motor and let the throttle slam shut, the vacuum level will rise significantly and you'll end up sucking all of the mercury out of the tool and into the motor. Obviously, if you are using gauges, this isn't a concern. If you move the throttle slowly, you will avoid that high vacuum condition.

Ideally, all 4 level (or gauge readings) will be the same or as close as possible. If not, it's time to make that so.

Go ahead and make the adjustments. A little adjustment makes a big difference. You should not have to turn that screw very much, one way or the other. Watch the manometer and try to get those 2 carbs as close as possible. Now you know why I told you to pay attention to which hose is connected to which carb.

All good? Button it up, set the idle back to 1,000-1200 RPM, and go for a ride. If the synchronization was off, you should notice a much smoother idle now. Congratulations, you just saved yourself from paying someone $100 to do that job.
While you're in there, you might as well run the plugs out and see what kind of shape they're in. Check the air filter, too.

Man, this made me thirsty...