My car is Cultus 2002 and it has 95+ k kms and the problem is that i usually drive my car on CNG and never on petrol but sometimes once in a month i drive about a km on petrol,so today when i started the car on petrol,it was throwing water from silencer(Which is the good sign i guess?) but it was also giving smoke from silencer little bit when i press the acceletor and on CNG no smoke but water from silencer and no burning of fuel,on the other hand i need to know that why the sound of "phak phak" like something is bursting in the engine,the sound like that is coming on both, Can you please help me with this?