2007-2009 Yamaha F15/F20 Outboard Service Manual, Page 297Get this manual
5FUEL SYSTEM 1) PRIME START SYSTEM
Prime start system by PTC (Positive Temperature Coefficient) heater valve is used onWhen starting cold engine, the wax is condensed and the plunger is fully pulled in to discharge the fuel for obtaining rich mixtureAfter starting the engine, the stator coil continues to supply electrical current to PTC heater to become feverishThen the wax is expanded due to fever, and the plunger is pushed out to close the starter jetAfter the starter jet is completely closed, the carburetor is normally operatedPTC heater becomes feverish when the electrical current is givenHowever, when the heater temperature is reached to the specific range, PTC heater changes to nonconductor and stops heatingWhen the heater temperature dropped, PTC heater changes to conductor and restarts heatingTherefore, PTC heater can keep the constant temperature even if the electrical current is continued to supplyPTC heater Wax