I recently purchased a 2007 Honda CRF250R. It was "popping" or "backfiring", and I was told that the bike had been run in Colorado the week before and had a new main jet put in it for the high alltitude. I'm from oklahoma, so I went to Honda dealership and asked for a factory stock main jet, they provided me with a 160 main jet. When I went to replace the main jet, I discovered that it was a 172 main jet. Does anyone know what the main or stock jet is for a 2007 Honda CRF250R? From what I can find the factory stock jet should be a 175 but Iam not sure. Also the bike is very hard to start and I dont know why.