I don't think the 10% ethenol is the problem, as noted earlier it's been in use here in Colorado for about 15 years. Most likely, it is the new botique formulations the EPA is pushing on us that vary by differnt areas of the country.

Most of these vaporize at lower temperatures which is not a big deal if you have a fuel injected car because the fuel is under 30+ PSI pressure, but with a carb, and only 5 psi pressure the older cars vaporlock and boil the fuel much easier.