WOW!!! what a difference a little grinding can make.
This is my first motorized bike build and I didn't want to go crazy right out of the box. I did your basic port and polishing and gasket matching on both the intake and exhaust. I rode the bike for about 50 miles and then had a funny little mechanical problem where a foreign object jammed the clutch and crank gear, no major damage. I had the engine apart so I figured I would take the internal modifications one step further and notch the intake side of the piston. Wow!
I'm still running about 14 and a half - 15 to 1 ratio on the fuel mixture so she tends to be a little sluggish but the low end torque coming out of a turn now is at least 15 to 20% better with this one modification. Without a doubt if you buy one of these kits notching the intake side of the piston is a must.