Just some advice when tuning.
What I do here is tune for best idle quality, smooth off idle, and at light part throttle. Then go to the track and tune the secondaries for best ET/MPH. This often takes a few tankfuls of fuel, and some extensive street driving under various conditions, and a couple of trips to the dragstrip. The goal is to find out what your combination of parts wants.
I go after the jet size first, heavy part throttle for best power climbing steep grades, lugging the engine without the secondaries, etc.
I tune part throttle with the APT next, going lean then richening it up till I find the best setting.
Full throttle last, and never touch the primary side, secondary rods and maybe a hanger change only.
After you have found the very best settings, hook up your analyzer and see what these settings are. Those are your baselines. Regardless what you see on the meter, you have to give the engine what it wants for best performance in all areas.
I shelved my meter years ago, once I figured out how to tune without it. I don't completely trust them either. The most accurate units have the sensor a few inches from the cylinder head, and one would really need 8 of them on a V-8 engine to see the most accuracy.
One thing I've learned over the years, is that lean part throttle setting(s) seldom delivery the best fuel economy in the big scheme of things. This simply happens because of the varying conditions the vehicle must operate in. It also is going to take a specified amount of energy to accomplish this task right to start with, so you can't get around the basic laws of physics. Every time I've tried going lean on the part throttle, I had to drive like a 90 year old lady to improve the results, pretending the entire time there was an egg under the throttle and I was going to break it if pushing down too hard.
Several years ago I had to commute 600 miles one way to see my family as I was displaced from them for job related reasons. I'd make that run at least once a month for a couple of years. I had a 1979 Chevy Blazer with a fresh 400cid SBC engine in it, and tuned to perfection. That 600 mile run gave me buttloads of opportunity to mess with the APT, and I even changed jets several times. The ride involved driving from Ohio to Virgina, down Intersate 77, which is full of hills and curves, then down thru the Blue Ridge Mountains in Virginia.
Every single time I leaned up the carb to where it ran flawlessly on flat ground, fuel mileage was worse on that 600 mile run. The engine ran fine at light load, and on flat ground did every so slightly better in fuel economy. As soon as I started driving it under heavier load, it used more fuel with leaner settings. At first this puzzled me some, as like most folks, I associated "lean" with efficiency. What really happens is that with lean settings and light load, the distributor vacuum unit is applied, and the engine can tolerate the lean settings and light throttle opening. When load is applied, the vacuum unit retards the timing, as throttle angle is increased/engine vacuum falls off. This mandates more fuel from the carburetor so the engine can keep up vehicle speed. With lean jetting, MORE throttle angle was required to keep the vehicle up to speed, so it consumed more fuel that it did with a richer calibration during those periods. I consumed myself with this testing, made the trip interesting as well logging all the numbers, and seeing the results. The ONLY time I ever got improved fuel economy with a relatively "lean" set-up, I had to let the vehicle slow down considerably on steep grades, and stay very light on the throttle. It made the trip long and "boring", and the improvement was so slight, it wasn't worth the effort(s).
When the smoke cleared and dust settled with my testing, I ended up right back at the very first jet/rod relationship that I started out with, which had initially provided me with a very slight lean "tip-in", and a jet size that delivered great heavy/part throttle engine power.......Cliff
