With larger aircraft like C150-C152-C172 if you want to burn automotive gasoline (Mogas), it best to add some additives to it once in a while, the lead in 100LL (Avgas) (once again according to my A&P mech) is supposed to be lubricate of some sort, and he suggested that if I wanted to goto the Mogas STC in the PA-28 to run a gas aditive every couple of months.
The biggest diffrence between Mogas and Avgas, is that Mogas breaks down quickly, sometimes in as little as 6 months (from when you buy it at the pumps) while with Avgas, there have been cases where they found a 50yo supply that burns just fine. Now this isn't a problem if you burn all you have quickly.
Oh at the glider port, we fill the on-field cars with 100LL, well lets just say none of them would pass emissions tests.
Man talking about this is giving me gas...
At worst, you screw up and die.