Yes the Mothballs did work, back in the day. Yes they did clog fuel lines and filters, that is why we mixed it with the gas then strained the gas to clean out the pieces, then added to your gas tank.
Why doesn't it work today? There are several reasons.
1. We used Leaded Fuel. You know the stuff that smelled good not like the stuff we use today.
2. No fuel injection
3. No smog controls or Computers.
4. We were dumb kids grabbing at ever horsepower we could. Damn the engine, we can get another one. LOL