if its a briggs engine ther will be a small black wire on the back of the engine, diconnect this and try it, if it works then one of the safety switches is faulty, try removing the plug and turning the engine over for about 15-20 seconds then putting it back and re trying?? if not id try changing the plug even if you clean it some show a fault within weeks!! an RJ19LM or B2LM plug is suitable,