carb and backplate is one piece. one of the key things with this motor is rotor clearance. more than likely the rear face of the case will have to be machined down. you will want .002 to .003 total clearance.you may have as much as .020 out of the box. also make sure the od of the rotor is not rubbing on the id of the case. litely use a needle file to deburr the drive slot hole so the rotor will drop on and off the crank when dry,it needs to float. set rotor closing to about 65 degrees after tdc. square up the inlet hole in the case, for more flow.if it has a double plug head, lose it. remove the carb extension. set exhaust to 187 to max 190,transfers to 127 to 130, shoot for 30 blowdown, head clearance about .012. if you can find someone with a wire edm have them oblong the carb bore wider with a small corner radius,don't go taller,or carb won't shut off. HAND LAP THE WRIST PIN BORE,with the wrist pin and some wd-40,till it works in and out,and rotates smooth, or it can sieze in the rod. tap water holes to lower chamber in case and plug with 4-40 set screws. these mods will make this a bullet proof motor for a long time, and will run,or out run current engines