RE: ryobi 31 modification
no. the 11.11 walbro carb fit exactly to the back of the manifold. i just made a spacer bc the carb throtle would hit the backing plate. but the spacer was good cause of the added torque it added. but as far as the reed valve goes. if you take the backing plate off you will see the reed valve and a bent piece of metal on top of it. take pliers and bend it away from the valve just a little. i have heard 1/8 of an inch. i just bent it till i thought it looked good. lol. but DONT touch the reed valve. this allows the valve to open further and allow the fuel to rush in smoother.