My dad gave me a bottle of Star Tron Fuel Enzyme treatment to try out. He's been running it in his bike and any other small engine he has and they all fired right up this spring, no carb issues. I gave it a shot in my motorcycle and it seems to really be working. The bike doesn't pop anymore and seems to rev smoother through the RPM range. Here's the product:
Seems to be working for me so I figured I'd pass it along.