I don't post a ton here, so many of you may not know who I am, but to keep it short, I own a performance Ford shop in NY and specialize in dyno tuning for both EFI and Carbs. Just a little disclaimer before I type my response, that I know a thing or two about A/F and tuning
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A quality Air/Fuel meter is probably the best money you could ever spend on your car. Obviously proper A/F is essential for a heathly motor at WOT, but knowing your A/F at idle and part throttle can drastically improve driveability as well. There are many A/F meters on the market. The ones you want to stay away from are the ones that tap into stock oxygen sensors. That's probably not an issue for carb guys, and they'd need a complete kit, but I say this for the benefit of the EFI cars here. You want a true wide band A/F sensor setup. Now there are lots out there, and I've used most of them. Right now the hot setup is the Dynojet Wideband Commander. This is the most complete setup on the market, and it's got a great price as well. It comes with a gauge you can mount in the car, but if you don't want an extra gauge, it can also datalog in real time, which you can then download to your home PC and check out the readings. Full info on the Dynojet WBC can be seen at
www.widebandcommander.com. I sell them and I did a group purchase for them on the FFR forums not long ago. I can get them for anyone, but I really don't want to get too much into that here because I'm not a supporting vendor. But I'm more than happy to help anyone out if they want to contact me privately.
As for the tuning end of it, tuning carb motors is not hard, just time consuming, since you have to pull the bowls on and off to change jets. And you guys are correct, that big jet changes seem to make small A/F changes. Here is an example... I had a Superformance on my dyno last week. It had a 392 stroker in it. The owner (who posts here and may chime in) had a bunch of head work and new cam and such added to the motor, but never dynoed it since the new work. First pull on the dyno, the car was over 14:1 A/F, which is too lean. Optimum A/F for a pump gas NA motor is about 13.0-13.5. He was running a Speed Demon 650 carb, and it had 70 main jets on the primary side. I switched up to 80s, and the A/F only dropped down to 13.2. Luckily that was the perfect A/F, so we left it like that. The car also picked up about 10hp and 15 ft lbs. Now aside from the WOT tuning, I noticed the car was very "lazy" off idle as well, and it didn't have good part throttle repsonse. A/F showed it was really lean at idle. I adjusted the idle mixture screws until I got about mid 14s on the A/F (this is where EFI cars run when in closed loop as well). After adding in some idle fuel, the off idle throttle response was DRASTICALLY improved, and it was much easier starting the car off in 1st gear now.
This is a few basic ideas behind tuning and A/F meters. I hope I helped shed some light on it for people, and I'm always happy to help you guys out if you have tuning questions.
Sal