[Cliff R]

"The fuel pump is a carter competition mechanical pump."

I tried one of those about 20 years ago with ZERO success. It did much as what you are seeing here. It also really didn't offer any improvement far as keeping the bowl full on hard runs over the stock pump. One of the big reasons for that was sucking thru the stock lines and sump. These "high performance" mechanical pumps REQUIRE improved fuel delivery or they may not work much if any better than a stock pump. I see this all the time with this sort of thing.

One of the symptoms I had was intermittent flooding especially after a hard run. I put a pressure gauge on it and found it was all over the map, varying from about 7 to as high as 12 psi. I got rid of it, went to an electric pump with a regulator and ALL the issues went away.

As far as the A/F ratio it really doesn't matter. We tune for results, not a specific A/F number. The carburetor is a "load sensing" device and responds to throttle angle, engine load, and air flow thru it. A/F can vary greatly over the load/speed range of the engine. Nothing uncommon to see between 13 to as high as 17 to 1 A/F in the "normal" driving range. As it relates to this discussion just had a customer call all upset that he was seeing as high as 17.9 to 1 A/F at very light engine load with his new build and all worried he was going to hurt something. I asked him about engine performance and fuel economy, surging, lacking power, etc? He said it ran FLAWLESSLY but the plugs were kind of white. He also noted getting upwards of 17-18 mpg's with a 455 in a later T/A w/o overdrive. I told him to put tape over the gauge or get rid of it.....

A/F meters should be installed and a piece of black tape put over them. The tuner should then tune for best results in all areas, then remove the tape and use the numbers for "base settings". You can and will drive yourself nucking-futz chasing an A/F meter around. Folks also forget about the distributor, especially the vacuum advance. BIG player for fuel requirements at light engine load and should be part of the tuning process.........FWIW......Cliff

[Formulajones]

Originally Posted by Navy Horn 16

Pump gas can be up to 10% Ethanol. That's all you know about your pump gas, other than the octane level. How much actual ethanol that is in your gas will vary from station to station and tank to tank. It depends on how much ethanol cost at the time they were blending, how much RINs cost, how much the blender was willing to pay for carbon offsets, and several other factors.

There are bean counters and chemists working at the refinery to make sure the right blend of gasoline and ethanol makes it to the premium and regular tanks.

It isn't something that you can tune your carb around. That's why I run a mix of 90 octane ethanol free and 100LL. Ethanol has less energy per unit of volume, so you can make more power by getting rid of it from your fuel system.

Actually you can know more than that. They have made small ethanol test kits for years. Cheap to buy and probably still all over ebay.
Back when I was testing that stuff, I found as much as 17% ethanol at pumps that were advertised at 10%. There was no real consistency that I found. You can tune and crutch it to some degree. In order for a car to run properly on it the circuits have to be modified. Mainly the idle circuits have to be richened, and it's a good idea to run the engine a little on the rich side of stoich to cover any inconsistencies.

But the real point of my post was to elaborate a little on what I felt Steve meant.

[STEELCITYFIREBIRD]

Originally Posted by pmd400

I took the firebird out today to tune the carb. I recently installed a 17056262 qjet. AFR at cruise is about 15.5:1. WOT is about 13.5:1. After WOT the cruise AFR goes to 11:1 for a few minutes before it leans back out to over 15:1. What could cause this?

really that long??
have you tried returning to idle to see where it goes??

[pmd400]

Originally Posted by STEELCITYFIREBIRD

really that long??
have you tried returning to idle to see where it goes??

I was on a 100km/ph road so I just drove through it. I didn’t want to stop in case it flooded. I’ll retest again on the weekend.

[pmd400]

I find the afr gauge to be helpful. You might set the engine for best idle and it turns out to be 13:1 afr. But it can then be leaned out to 14:1 and there be virtually no difference. Also with light throttle cruise, the afr could easily be 13:1 and it feels fine, but leaning it out to 16:1 has no negative effects

[77 TRASHCAN]

Ttt