I have accidentally added petrol to the oil tank of a petrol mower I could not find and opening underneath the tank and so tipped it upside down to drain the oil tank ,and then added fresh oil it did work for a little while but now doesn't want to start or it does now and again only for about for 30 seconds and then stops with a fair degree of smoke,could anyone offer me any advice I did have a look at the spark plug and it looked to be quite oily I don't know if this is supposed to be like that,maybe tipping the mower upside down helped oil to spread to other parts of the mower unintended