I think I understand the idea here. Moth balls are made of naphthalene, which is basically two benzene molecules that are connected. Though naphthalene isn't flammable, benzene is. I suppose it's possible that being dissolved in gasoline, or the conditions inside the engine pre-combustion could cause the naphthalene molecules to break apart into into benzene molecules, and thereby improve the combustion characteristics of the combined fuel mixture.
If this is the case, it could work similarly to nitrous oxide, which is not technically flammable by itself, but provides an elevated amount of oxygen to the fuel in the cylinder when it's broken down by the pressure/heat during compression. More O2 plus + more fuel = more power.
I really don't know for sure if this something I would test out myself, but I know benzene was used as an additive in gas in the post-WW2 era. A number of non-english speaking countries even use the two words (gasoline and benzene) interchangeably. In German specifically, gasoline is called "benzin".
Hope this makes sense without being too wordy...
