1st flight of the day and the engine was all of a sudden rich, last week it ran fine, now some background information, last week was 87 octane 10% ethanol ,32 to 1 pennzoil, this week was 89 octane no ethanol,32 pennzoil, which do you figure was the culprit the octane increase or the lack of ethanol? either way a little tweak on the needles and its running fine again, as a side note my daily driver gets 17.1 mpg with the 87 and 19.4 with the 89, before everyone asks why i changed the gas on the plane , the local station was out of 87

Could be other factors too, but changing octane doesn't change the fuel/air ratio. Going from 10% ethanol to 0% ethanol does change the fuel/air ratio. More ethanol by volume is required than gasoline. So the engine goes rich when going to straight gas if the needle was set for a mixture containing ethanol.

The loss of ethanol automatically made the mixture a minimum of 3% richer. A new batch of slightly higher octane gas probably helped the issue along by slighly delaying the burn process.

Yep, and your car got better mileage because the computer was able to advance the timing more with the higher octane fuel. When an engine starts to experience detonation, the computer pulls timing out of the engine till it stops. That hurts gas mileage and performance.

AV8TOR

My mileage can vary net 5-10% depending on where I fill up. Gasoline mix and quality is a moving target, there is no formula set in stone.

Another 100% correct assessment.

My father used to own a service station. Gas companies used to be proud of their fuel, and competed to offer good quality gasoline and offered incentives to people to buy it. Remember when they gave away things when you filled up? I remember one promotion whereby the attendants cleaned the interior of any car that got a "fill up". (I know, I'm dating myself here...)

Nowadays, the prevailing oil company attitude is

"You're lucky we are selling it to you at all, even at 4 bucks a gallon, so take what you can get and shut up!"
"If you keep b**tching, we'll just do another contrived shortage to shake you up!"

AV8TOR

Screw you, I remember CLEANINGout any car that got a fill up! I didn't think I was old yet and here you are calling me names by proxy

$1.35/hour for wages, pumping gas that sold for $0.24.9/gallon, washing windshields for a $1.00 gas sale while also checking the oil and tire pressure. For every car that came into the station. If you failed to do it the customers complained loudly and you soon sought other work. Unless it was an MG or Stingray the dash was too high for a good interior view. Yea, I remember. Free glasses, cups, Green and Blue Chip stamps, collectible figures, bobble head dash dolls, etc. Once in awhile you encountered a wild one and got to pump ethyl.

And every once and a while, if you were lucky, the view through the windshield while you were washing it was quite good!! (Luckily I am tall!)

AV8TOR

Ahh .. those good old days in the sixties. I could drive over to Juarez, Mexico from El Paso, Texas (a 15 minute drive) buy gas for 10 cents a gallon, get a haircut AND a great carwash, leave a tip and only spend $5.00! The gas always smelled/burned nasty though because of the higher sulfur content.