There is a jam nut that has the spray bar assemble locked in place. You will need to loosen up the jam nut and the whole spray bar and needle valve will unscrew out. Install the new one by screwing in the new one. You will want to get the spray bar close to centered in the carb, then just tighten up the jam nut. This should not effect the break in off the engine at all. Good Luck, Dave