Yamaha F100B F100C Outboards Factory Service Manual, Page 21Get this manual
Features and benefits Technical tips Carburetor
Prime start To facilitate the starting of cold engine, an air-fuel mixture that is richer than normal is requiredFor this reason, the Prime Start system has been adopted in the F100B and F100CIn the Prime Start system, the thermo heater plunger is in position that fully opens the fuel enrichment valve while the engine is being startedThus, fuel enrichment is achieved during the starting of the engine, and continues while the engine is being warmed upOnce the engine is started, signal is sent from the pulser coil to the CDI, and from the CDI to the Prime Start to allow the wax to expandThe expanded wax moves the thermo heater plunger in the direction to close the enrichment valveAs result, the volume of fuel that passes through the fuel enrichment valve decreasesA few minutes after the engine has started, the thermo heater plunger completely closes the fuel enrichment valve, thus ending the fuel enrichment by the Prime Start system1 5