One of my students called me to help with an engine that wouldn't start after a rebuild. He had tried everything, including all the telephone troubleshooting tips I could think of. I went to his home, double-checked all his work, and it was right on. No start! I pumped a little gas from the tank into a coke bottle, poured it out on the ground, and tried to light it with a match. It wouldn't burn! Fresh gas fired it right up! This car had only sat unused for about 3 months, and the gas went bad! Still don't know why!
Jerry