Johnson Evinrude Outboard Motors 1956-1970 1.5-40hp repair manual., Page 91Get this manual
4-1 INTRODUCTION The carburetion and ignit ion principles of two-cycle engine operation MUST be understood in order to perform proper tuneup on an outboard motorIf you have any doubts concerning your understanding of two-cycle engine operation, it would be best to study the operation theory section in the first portion of Chapter 3, before tackling any work on the fuel system4-2 GENERAL CARBURETION INFORMA TION The carburetor is merely metering device for mixing fuel and air in the proper proportions for efficient engine operationAt idle speed, an outboard engine requires mixture of about At high speed or the mixture may parts air to part parts air to part fuelunder heavy duty service, change to as much as 12 fuel
Float Systems small chamber in the carburetor serves as fuel reservoirA float valve admits fuel into the reservoir to replace the fuel consumed by the engineFuel level in each chamber is extremely critical and must be maintained accuratelyAccuracy is obtained through proper adjustment of the floatThis adjustment will provide balanced meter ing of fuel to each cylinder at all speedsFollowing the fuel through its course, from the fuel tank to the combustion chamber of the cylinder, will provide an appreciation of exactly what is taking placeIn order to start the engine, the fuel must be moved from the tank to the carburetor by squeeze bulb installed in the fuel line