I understand that but when I removed the old fuel mixture screw with no O-ring, spring or washer came out with it and when I put the new one in with a O-ring on the shaft and then thurn the screw out 2 turns and tried to start the bike all it would do is backfire and not run at all. I put the old one back in and it back fired once and started right up. That is what I don't understand. The only thing that I can think of is that the new screw is not the right one. I did notice that with the new one that when I seated it and then turned it 2 turns, it was real wobley and real loose. Thanks for everybody's help.