you mentioned on another post you are using outboard motor and someone has already told you that that is your problem. get some bike oil and use that, if you are premixing, make sure your oil injector pump is disconnected so you are not getting a double dose of oil.
remember that the more oil you add per unit fuel the less fuel per unit of mixed gas you have because the oil takes up a percentage of the volume, so, too much oil means you run lean on fuel, although you may still be fouling plugs with oil. and not becasue you are too rich with fuel!