I have a 2000 300EX that i bought from a friend. It has a K&N filter ( airbox is stock no modifications). A Big Gun race series slip on silencer. Pipe is stock. Everything else is stock on the engine. The carb was jetted by someone. I dont know if it was my friend or not. But anyway It wasnt running all that great when I got it. So I figured the jetting may need some adjusting. I believe that the stock jets are 122 main and 38 pilot. However when i took them out the Pilot is a 40.. not unreasonable I think. But the main was a 142... and it is a Keihin jet... I know some companies use different numbers but this should be along the same line as the original since it is a stock brand... Now I am thinking maybe it should be more along the lines of a 125 or 128 at most. I need some input on this. I am not really a jetting whiz. But I do know that 122 to 142 is a crazy big difference. Any help on where to start???