What happened to gasoline in the mid 1970s?

WHERE is the measurement for unburned fuel?
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the amount of hydrocarbons "flashed" from evaporation pales in comparison to those released when fuel is burned.
I'll go with the info @MOPOWER linked to for whether they were generally in the same order of magnitude.
But my nose tells me that in the Spring (like now) I can often smell the fuel vapor on both my '67 (no vapor capture) and my '85 with its vapor capture system mostly all there.

Somewhat related was what I thought was a veery interesting discovery was how much vapor even an open air cleaner captures when an engine is running at idle.
This is screenshot from a datalog where I removed the air cleaner lid while idling in the Summer.
Yellow markers on timeline are when the air cleaner lid was removed and then reinstalled.
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Recording time in min:seconds along bottom.
There may have still been some winter fuel in the tank. I'd have to look to check that.

i think the reference is to unburned fuel in exhaust. The theory is that the stoichiometric ratio is never perfect and the mixture doesn't completely combust there by leaving unburned fuel in the exhaust stream.

I think the reference is whatever the person writing about wants it to be, whether its the stuff out the vents or the stuff out thte tailpipe. Its all good discussion. :) But I too was focusing on tailpipe.

The cat converter is there to process unburned hydrocarbons and convert the gasses to inert gasses by way of catalyst
Looks like you're correct. The first generation of cats did reduce HCs as well as CO
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What money is in ethanol that is motivating the government?
There are two main groups that are (or were) lobbying for ethanol, and there may be others.
The automobile manufacture's were pushing for fuel changes that would help them meet both emissions and better corporate fuel milage overall. Do some web searching for Reformulated gasoline and ethanol and you'll find everythiung from academic papers to trade industry backed promotional/educational material.
Ethanol is an oxygenate and it can improve milage if the car is set up for it. I'll say this. This current generation of E10 RFG runs a heck of a lot better than the MTBE stuff we had for a few years. That stuff was horrible (and pretty toxic too).

According to the timeline, Calf banned MTBE in 2004, and the Federal oxygenate requirement was dropped in '06. The concept (as I understand it) was that the car companies only needed it for a few years to bridge the time needed to develop and produce slightly higher milage and lower emissions cars and trucks.
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However at the same time the oxygenate was dropped, the "Renewable Fuels Standard" was implemented.
One perspective is the reason given on the timeline. Another is that the corn producers and industries that had grown to support the need for eth in fuel didn't want to see it go away.

We are 37 years later and cars are still not doing way better. They should be doing way better.
Yea I agree. It seems kindof ridiculous how poor the fuel milage is on many vehicles today that have the benefit of more than 3 gears in the transmission. I think part of it is perceived safety and 'comforts' and all that stuff that adds weight.
Ironicly it seems to me behaviours have changed a lot too. I see a lot more people sitting in their cars with the engine idling than when I was kid. Now maybe its location not time related. Dunno. Just my observations.