[Formulajones]

Originally Posted by Cliff R

An A/F meter or plug reading is not needed for tuning. A mentioned it's difficult, if not near impossible to read plugs on this piss-water ethanol enhanced crap anyhow.

Tune the primary carburetors for best idle quality at the leanest settings.

Tune the jet size for best light throttle and part throttle power, smoothness and fuel economy. As you lean it up stop going lean when the engine starts protesting the leaner mixtures. Fatten it backup till it runs the very best without excessive fuel consumption.

It may take several attempts to nail down the correct jet size. Don't forget that the vacuum unit is also a big player in light throttle tuning, and adding advance will burn leaner mixtures without loosing power, but there is a point of no return with these things.

For the end carbs, you need a chassis dyno or drag strip to find out exactly what jet size is most ideal. I'd stay pretty rich in that arena as there are no negatives anyplace from a little too much fuel, but BIG negatives when you go too lean, as EGT's rise quickly and detonation will destroy the very best prepared shortblock.......Cliff

WOW, that's like tuning in the dark Cliff. Why make a dozen attempts at leaning things and going back and forth when wideband would get you spot on in just a few minutes, and then you'll know exactly where you're at.
You'll never know if it's safe (or rich enough) without the wideband, which a chassis dyno would use. The best in my opinion because you can find that AFR where the car is happy under load and makes best power on a SAFE tune.
The dragstrip, although fun, isn't exactly the best method, although I've done alot of this, trying to watch MPH on each pass and tune properly would require having a handy weather station to keep track of DA numbers as they can change every 30 minutes and affect the performance of the car. Not to mention wind direction and speed changes will affect MPH too, AND, you need a car that is consistent enough at the 60 foot mark. You can get them close, but these variable can throw you off, and the average Joe can't pull all this off succesfully. Then lets not hope someone isn't trying to dial the car in on a day with 4,000 ft. DA numbers, then goes back in the fall with mine shaft air and suddenly the car is dangerously lean.
I've had some cars that run their best at the track and then find out later the AFR was 13.2 or 13.6 at WOT. They almost always make more HP when lean and that shows up with MPH, but is it safe? Without the wideband they would have never known.
If a chassis dyno is out of the question, I prefer the wideband AND the track. I can tune to the MPH, keep track of weather conditions, and watch the wideband to see how lean I'm getting. I'll get to a point and stop when I feel I've reached a safe limit on the AFR, even if the car is still picking up MPH, because I prefer to be a bit on the fat side with todays crap gas.

[Cliff R]

We tune for actual results, not what a meter tells us. Folks continue to believe that "lean" settings with this hobby are going to produce improved fuel economy, more power, etc. That is usually NOT the case. Numbers are ALWAYS for reference, as these engines operate in a pretty broad range as far as A/F ratio goes, and there are many other factors at work here beyond just main jets. Some engines are also a LOT more efficient than others, and will require less fuel to do the same amount of work. A full throttle A/F reading for some racers using engines with really high VE may be up near 14 to 1, where a hobbyist with a piss-poorly chosen combination of compression/cam/quench distance/intake/exhaust, etc may require 12 something to 1 A/F for best results.

I would also add here, that IF you find yourself making a dozen attempts to get the tune nailed down for jet size on a center 2GC carb, you were WAY, WAY off the mark right off the bench, or you'd better keep your day job!....FWIW.....Cliff