You can tell if your secondaries are opening by keeping them shut with a spring or other means.  Test drive the vehicle.  If performance is worse with the secondaries held shut, then they were opening when operating normally.  Winging the engine in neutral does not work!  Vacuum secondaries operate off engine load, not rpm, and there just isn't enough airflow in a no-load situation to open the vacuum secondaries.

Now that you've got the basics down, here is how you tell what circuit needs to be richer or leaner. You put an instrument in the exhaust flow that tells you graphically whether the engine is lean or rich. You then put a vacuum gauge on the engine to tell you what circuit is working at the particular time that you are lean or rich.

Simple!

The first instrument is known as an O2 (oxygen) sensor. These sensors are used in electronically fuel injected cars as a signal telling the computer whether to supply more or less fuel. O2 sensors create their own electricity in the presence of heat and oxygen. You simply put the sensor in a hot spot in your exhaust flow, then read the electrical output.

There are a couple of ways to put O2 sensors in your exhaust: The trick way, and the cheap way.

The Trick Way

Buy an air/fuel ratio monitor from Edelbrock or K&N. Summit (1-800-230-3030) sells the Edelbrock system for about $130. This comes with an O2 sensor, weld-on bung, and a display panel with yellow, green, and red LED lights representing lean, good, and rich mixtures.

Racer Wholesale (1-800-886-7223) sells several different air/fuel ratio monitors. One has two channels for dual exhausts, and another has rich/lean and injector duty cycle for you FI guys.

The Cheap Way

Buy a single wire O2 sensor at your local parts house, make your own bung, and read the voltage with a digital voltmeter. The sensor that I bought is a Standard brand, number SG-12. The threads on this sensor are the same as a small-block Chevy gasket-style spark plug, so the bung can be made from one of those spark plug anti-foul adapters. Other O2 sensors use the large diameter threads of 18mm big Ford spark plugs. Just cut and fishmouth the adapter so that the sensor sticks into the exhaust flow. You need to put the sensor as close as possible to the engine so it gets hot and stays hot. Just make sure you route the wire so it doesn't get burned by the hot exhaust pipe. Weld the bung to the pipe, then drill and file the hole to clear the sensor.

Sensor installed in Pinto exhaust.

Sensor and welded bung:

Once you have the sensor installed and wiring run up to the inside of the car, attach a digital voltmeter (you really should have one of your own, but you can sometimes borrow these from friends if you don't have one) to the sensor and a good body ground. The sensor is positive. The readings you'll get once the sensor has heated up will be from 1.1 volts (1100 millivolts, or mv) down to about 100 mv. The high readings are rich, the low readings are lean. The perfect mixture for cruise is 400 mv. I have found my car to run well at about 700-800 mv. Once it gets below that, it tends to get into a lean misfire. Your results may vary.

Here is a general idea at what the O2 sensor voltage output looks like. As you can see, the slope around 400mv, which is 14.7:1, or perfect combustion, is very steep. This is why only computerized fuel injection systems can really hold anything close to 400mv. If you're wondering about how a sensor can read oxygen content in rich mixtures where there is no extra oxygen, the sensor begins to act as a temperature sensor above 400mv.

Vacuum gauges

You will need a gauge to read the manifold vacuum on your engine. The more accurate the gauge, the better your results will be. The manifold vacuum is measured at the base of the carb or on the intake manifold somewhere. Don't tap into just one runner, though, as sometimes this will give funny readings. You need to check the signal that sees all the cylinders. Most Holleys have a manifold vacuum port in the front on the passenger side under the primary float bowl.

Road Tuning

Start by taking your carb apart and writing down the sizes of the jets, the actuation point of the power valve, and the size of the accelerator pump squirter. Put it all back together, check for leaks, then drive it until the engine is warm. In order to get good readings, you will need to drive at a constant speed of 45-55 mph, accelerate lightly, and accelerate heavily.

Idle

The best way to set the idle mixture is to lean the carb out until the vacuum just starts to drop, then richen the mixture by about 1/4 turn. If you have a bit of a stumble in very light, low speed operation, sometimes it helps to richen it up by another 1/4 turn.

Main Jetting

Going down a flat road at a rate of about 45 mph or higher will give you a good indication of your main jet sizing. Shoot for between 400 mv to about 700 mv. Since carburetors are not as exact as computer controlled electronic fuel injection, keeping at the perfect 400 mv will be tough. You always want to go a bit rich, as excessively lean mixtures will cause damage to your engine, create pollution, and give you bad gas mileage and performance.

You can do this without a meter, but it's a bit tougher. Start with the factory jetting and proper float levels. Drive it around for a while, noting if the engine surges at highway speeds. Take a look at the plugs. If they are sooty, you may need to lean out the main jets. If the plugs are white, you may need to richen the main jetting. Start stepping the jets up or down, one step at a time, and drive the car around for a day or two. Do not make large changes on your jetting. You can't just throw any jets in there because you think it needs to go one way or the other. It takes time to get it right, and you must change jets one number at a time.

All information above courtesy of: www.bob2000.com

My thoughts and gathered info: a HEATED O2 sensor stuffed up the tail pipe would work better than your nose for those of us that have no desire/way to weld in an O2 sensor.