look at the two angles cut near the piston skirt relief...these are cut to align with the internal case ports and redirect or directly force the air/fuel charge where it belongs.....im not tryin to sell backplates, im tryin to help anyone out thats willing to take a lil time and hand fit the os xzb round backplate to the case ports for phenominal results....look down into the case with the p/s removed and the bplate installed...mark the backplate in accordance with the case ports and start filing...you wont be unsatisfied I promise...this is the same procedure done at ebmods for vzb/bo1 bplates on his full mod versions...Idk why os doesnt do it, but they certainly should...
xzb blue head or bo2, will greatly benefit from a speed version head button (smaller cc combustion chamber=more power, and shaped specifically for smoothness), and the backplate mod...runtime, idle down and idle, tuning window, power, and smoothness are all upsides without a single down...other than the $45 for the speed button, but ebmod v2 buttons for vzb were $60, so its still more than reasonable...blue head benefits from coated crank also but thats for longevity...