Poor hot idle caused by ethanol gas? Whaddya think?
the fuel that I'm using (87 octane unleaded, 15% ethanol)
That's a very high concentration; even some newer cars gag on it. Can you get 10% instead?
Do the fuel line mod (I just linked above) and make sure your manifold heat control valve and thermostatic air cleaner are both intact and working correctly. You might very well wind up making a carburetor heat shield;
here is a dimensional drawing of the late-'70s/early-'80s factory item (and more info
here . As you can see, it has pass-thru cutouts for the throttle cable and kickdown linkage, access for the middle manifold nut, etc. Originally made of 1/16" pressed asbestos; you'd want to make it out of a modern heat-shielding gasket material—just do asbestos you can.
What do you think would happen if I used ethanol free 91 octane gas?
Well…give it a try and see for yourself! If your only options are 15% ethanol regular or 0% ethanol high-test, you might experiment with mixing those two to arrive at a blend that gives acceptable idle/driveability without draining your wallet too fast.
