I am only a couple months into riding and have a 2004 ys450f. It was running fine last weekend, and this week I cleaned the air filter for the first time since I have owned it. It has a Uni filter, and I think that everything is totally stock. I am not sure what kind of oil was used in the filter before, but I cleaned it with carb cleaner and oiled it with Notoil a few days ago. Upon starting it today, it would not idle and would backfire when revved. Is there anyway that the combination of Notoil and residue of the previous oil could cause the filter to not pass enough air? I have since learned that it is not a good idea to use Notoil on Uni filters, so I will have to buy some Uni oil, but I find it hard to believe that is this problem. Any help is much appreciated.