There has been trend toward using motor gasoline in aircraft engines. Gasoline engines intended for use in aircraft were designed for and should be run on one of the ASTM specified grades of aviation gasoline. Most major engine manufacturers specifically exclude motor gasoline from the approved fuels list. For a number of reasons, the use of motor gasoline in aircraft in NOT recommended.
Motor gasoline is manufactured to much looser specifications than that of aviation gasoline.
Quality and performance vary widely from refiner to refiner and from location to location. Quality control and quality ensurance in motor gasoline is much less stringent. The risk of contamination is also greater due to less careful handling. Also, many components of motor gasoline, especially detergents and oxygenated fuels, are quite variable in type and proportion and are generally not known or readily detectable. Motor gasoline has a much wider distillation pattern than avgas.