Furnace Short-Cycling

I pulled out the orifice. It looked clean and clear, no noticeable debris. I blew out the inside of the valve with an air compressor. Put it back together and it worked fine (just like it had every other time I've messed with it, only for the problem to return). I tested it for 2 consecutive days and it's still working OK. I have not received an answer from Dometic as to the purpose of the piece inside the exhaust pipe vent. Doug's understanding that it is to prevent water intrusion makes sense.