My RD 350 is model vith engine 31K.The year of produce is 1986.Problem is with acceleration from stops to speed.The power from the border 4000-5500 RPM is missing.I need long time go over this magic point.After 6000 to 10000 RPM have the engine full power.I tried adjust the float level to 21 mm. No effect! Can me anybody help how fixed the magic problem?