1969 Evinrude 40 HP Big Twin, Big Twin Electric Lark Service Manual 4596, Page 24Get this manual
cCheck throttle and choke shafts for excessive play Check operation of choke and throttle valves to be sure they correctly shut off air flow, yet move freely without bindingReplace carburetor body if valves or shafts' are excessively worn or damagedNOTE The threaded edges of the choke and throttle valve attaching screws are staked during carburetor assembly to prevent loss during operationDisassembly of these valves is possible, but replacement of the carburetor body is recommendedCORE PLUGS If necessary, remove core plug to clean out slow
Figure 3-13Needle Valve Seat Wear NEEDLE VALVES aInspect the tapered end of the needle valves for grooves, nicks, or scratches; replace if necessarySee Figure 3-14bDO NOT attempt to alter the shape of the lowspeed needle valveCARBURETOR BODY aClean out all the jets and passages, and the venturi, making sure no gum or varnish deposits remainDry after cleaning with compressed airKeep clean for final reassemblybCheck all gasket surfaces for nicks, scratches, or distortionSlight irregularities can be corrected with the use of surface plate and emery cloth