Yanmar 2QM15 Bleeding Fuel System - HELP
If by "decompression mode" you mean shut down, this will cut off the fuel to the engine. Set the throttle to FULL fuel, and make sure the stop levers on in the run position.
Hope this helps.
PS If you are using the starter to crank the engine make sure it does not become hot to the touch. If it does let it cool before continuing.