Mini Bike Engines

What are the coolest mods I could put on my 2 HP Briggs & Stratta engine. I use for my mini-bike, today I changed the oil, put a new spark plug, and took the muffler and put a straight pipe with an elbow

and if it was me id look around a 3.5 hp engine, because they weigh about the same. If you want to keep the 2 HP Briggs you can output port / polish the ports and put them in a major part sheared WHEEL to advance the timing. or maybe even put on a larger carb.