Hi I have a 20 hp mercury it's running real rough . I have cleaned entire fuel system . No matter how I set fuel mixture wont idle. Sometimes I don't have any spark. I have tryed everything I can so can anyone point me were to look next !
Disconnect the black wires with the yellow stripe from the switch box and see if it runs better. You will have to shut the motor off with the primer if it starts as those wires are for the kill switch.
I tryed disconnecting lack/yellow wires and it sputtered once and then wouldn't start so I reconnected them and still no start and found once again I lost spark ..
You are down to a couple of things either the pick up under the flywheel is failing. Or the switch box is going out or you have a bad ground wire somewhere.
One other thing do you have water on the plugs exhaust gaskets fail on those as they get older. There are also access plates by the throttle assembly that can cause a air leak
