You're absolutely right. Your motorcycle experience is a classic example of factory specs not working well on "older" engines...and that bike is less than 15 years old? Our cars are pushing 45 years and more...

But I'm not just talking about Ethanol...the changes in gasoline over the years go far beyond that recent development. Ethanol introduction is only one of many incremental changes that has occurred in gasoline over the years. Remember factory specs for these 68 Firebirds are also assuming you're running true LEADED fuel, of a different octane, without Ethanol, and without many of the other additives found in today's fuels. Not to mention substantial unknown changes as a result of environmental regulation which has resulted in different fuel refining and formulation methods, and different sources/grades of oil that it is produced from. Gasoline is produced with completely different methods, technology, and base products today, so therefore the end product is different today. Therefore different quantities are needed in order to get as close to stoich mixture as a given engine can handle when mixed with air, which changes jetting and adjustment needs...the flame front travels at a different speed than it used to, which changes ignition timing needs...resistance to detonation has been altered, which changes compression ratio needs...lubrication/cushioning properties are different, which changes valve seat needs...and ethanol is a whole separate topic not only with regards to energy output per unit, but also in the fact that it has changed gasoline into a dessicant that absorbs and suspends water instead of separating from water like it did in the past. Burning off trace amounts of water changes everything yet again (ever hear of water injection as a power adder?). And ethanol and other additives have the potential to react with plastics, rubbers, and even some metals differently from the gasoline of yore...

It's been nearly a half century since these cars had their tunes established by Pontiac. And gasoline of today doesn't even remotely resemble the fuel that Pontiac used to establish that tune...from ANY source. This means the tune that Pontiac established back then, as good as it may have been, is flat-out wrong for today.

What everyone needs to recognize is that if you or your mechanic use 100% factory service manual specs and parts to tune/build a FGF, and you intend to drive it, you'll end up with the wrong jetting, wrong carb mixture, wrong compression ratio, and wrong initial timing/advance curve/vacuum curve. Of course it will start, run, and drive, and it won't just blow up in your face. But it certainly won't be tuned anywhere near its potential, and it could actually cause some engine and fuel system damage over the long term....