Today I installed a 13.5:1 piston and now theres a problem. When im riding it down the street puttin it runs fine and when i rev it up in neutral it doesnt knock, it runs fine but when i get on it through 1-3 it starts to knock and run like crap. It gets worse as i go through the gears. i mixed Sunoco 110 and 91 at a 60/40 ratio. I checked my spark plug its white and i drained my oil to check for metal shavings and there is none but its already black. i figure im gunna have to tear it down agian to really check it out but before i do does anyone know what the problem might be from those symptoms?