The pressure regulator is defective or an injector is stuck open.
yes
leaking rings
If the fuel mixes with the oil it is because the engine is a 2 cycle engine rather than a 4 cycle engine. A 2 cycle engine has no oil reservoir and the engine is lubricated by the oil mixed with the gasoline. Without that oil in the fuel the engine would be destroyed. Now if you are saying that you have a 4 cycle engine and the fuel is getting into the oil reservoir, then I would suspect that the needle valve and seat are defective in the carburetor which is allowing fuel to flow into the intake while the engine is not running. This fuel will flow down into the combustion chamber and eventually end up in the oil pan. The float may also be sticking causing the same thing. Make sure to turn the fuel supply off when the engine is not running.
No, the flush oil is to clean the parts of the engine that are oiled. If you put it in the fuel tank it will block up tour fuel filters and your carburettors.
No #4 diesel fuel oil is for oil burners and will not ignite in a diesel egine
Bad piston rings. Get new engine.
Someone is putting it there. There is no way for oil to get from the engine to your fuel tank by natural means. Literally, if you have oil in your fuel tank, someone is sabotaging your vehicle by putting the oil there.
Engine running rich. Get this fixed ASAP and do not drive until you do. Serious damage will occur to the engine. If you have electronic fuel ignition and you pump your gas pedal before starting, this can add un-burned fuel to your engine oil.
What is the fuel to oil ratio for a mercury 9.9 hp 2 stroke engine?
Yes definitely! Do Not Run it!! If there is no oil in your fuel it will seize the engine. Because the oil in your gas is the only oil that lubricates your motor.
If the engine has an oil sump and an oil filler spout, it is a 4-cycle engine. On a 2-cycle engine, oil must be added to the fuel.
Someone puts sugar in your fuel, fuel runs through the engine, bingo bango bongo your engine will fail.