Honda BF20A-BF25A, BF25D-BF30D Outboard Motors Shop Manual., Page 26Get this manual
Engine speed does not increase
Stop the engine and check the water screens for cloggingIs the water screens clogging
{ Remove foriegn material and rechek
Start the engine and check the cooling system indicatorCheck with the engine idlingDoes cooling water constantly flow through the cooling system indicator?
Water pump is faulty Water tube is clogged or damagedDischarge port is clogged