Here's what happened. I started out this morning with my wr450, fmf factory 4 pipe and header, 170 main, 45 pilot, blue needle 3rd position. Bike ran great. I nromally ride at 3500 ft altitude in the desert of southern california Pipe was obnoxiously loud (105db) , so I put in the ama 96db insert. Then the bike ran ok. But it sounded fat and was not as crisp as I thought it should be. I checked the plug at it was very dark. So... I dropped the main down to 165 and changed to the red needle, 4th position. I put in a new plug also so I could inspect it later. Now, the bike is an absolute bitch to start. It runs rough at idle. At midrange, it runs ok, but tends to cut out on me at lower rpms. Can't get it to start at all once it warms up. this is very erratic behavior that doesn't make any sense. I am not yet doing any riding that would test the main jet. The needle should at least allow it to start easily. I am thinking of 1) checking the plug or going back to the previous one and 2) going to the 5th position on the needle instead of the 4th. Since I am not having problems starting, I am thinking that I might have a problem the plug, espeicially since I never changed the fuel screw or the idle. It should at least start up as it did before. Am I thinking about this the right way? Also, what is the real difference between the red and the blue needle. The blue needle looks bigger and would give me a leaner condition, right? How do they relate to one another (i.e. red postion 1 = blue postion ???) I am still learning about this stuff and trying to get it dialed in. Any insight is appreciated.