Your car will not have a carburettor, it will be single point injection (It looks like a carb though). Because a k&n has been fitted it's likely the breather pipe from the crankcase and/or cylinder head breather is venting to atmosphere. In your case under your bonnet and being sucked in through the heaters. Open the bonnet and loctae the pipe(s), they are black rubber about 1" wide. Either cut a hole in the k&n metal plate and push it it in there securely or put a small filter on the end. Alternatively secure the pipe lower down in the engine bay so the fumes go under the car.