Hi, I have just fitted a sportex cat back system to my 16v sporting and at the same time had a new front pipe fitted...ever since then every so often seems to start to backfire it sounds as if the exhaust is clogged??? One worry i have is that the front pipe is too small in diameter ...as every garage i went to said the sporting front pipe is fiat only but one garage said they could get one that would fit off a 1.1punto..so i dont know.....please help