I still don't buy it.
First - it appears that a well tuned car produces fewer unburnt hydrocarbons at idle
than at speed, which suggests that combustion completion under light loads is actually better.
Second, gasoline should vaporize more readily in the partial vacuum of light engine loads compared to higher loads because its boiling point decreases as pressure drops.
Lastly, do you have info about the surface tension of acetone vs hydrocarbons? I saw one reference (can't find it now, of course) that showed acetone's was actually slightly higher