I've seen Briggs & Stratton supercharger kits before. But this is the best yet.....Fill this up with 6 canisters of N20.
If you're wondering what it is, its a whip cream maker, like the ones they got at starbucks.
Run small diameter abs tubing to the carb, richen the fuel mixture and spray away. You will notice more power. Im not kidding, we did this on a 4 stroke 4hp briggs scooter about 4 years back. Total cost, about $60 and many cases of Whipit's.