I don't have first hand knowledge of this as we don't have to suffer emmisions checks here (yet)... but across the pond in Hongcouver they do have to go through "California style" smog checks. What I hear is that if you fill the tank with ethanol and retard the timing, you can make a car that had previously failed pass. (take a wrench with you to set the timing back when you are done). Depending on where you live, it might be tricky finding a gas station that sells ethanol. Ethanol is a gas/alcohol mix - you might be able to mix your own. I wouldn't be surprised if the magic potion I mentioned in my previous comment is just straight alcohol!
I hope that there are stovebolters out there who have first hand experience with this...
