So today I finally found time to take off my muffler and took a dremel to the manifold to make the opening bigger. I put the muffler back on and couldn't believe what happened! I am now able to cruise at 25 mph with 3/4 throttle where as before I was at about 18-20 mph. I got up to 30 mph and the SOB was still pulling like crazy! The engine sounded like it was going to explode from high RPMs so I backed off (w/ a 44t sprocket)! I can't believe the performance I got from such a simple and quick mod. I am wondering what else I can do to my engine to increase performance even more. This is the only mod I have made other than improving the chain idler. I have a 67 cc Power King and plan on getting a Champion plug and new wire tomorrow. What else can I do? Should I port the intake manifold too? I am thinking about getting a 40t rear sprocket so I can cruise at 30+ without blowing my motor up. I appreciate your input!