fe600racer, If you do a search, you will find many ideas and experiences on modifying the FCR carb. I did a lot of fooling with this carb, and listed it on this site as "$40 FCR spruce up". I essentially set my carb up like a 2006 Honda CRF-450R, since that bike did not need to satisfy EPA mandates. This included carb needle, acc. pump kit, jetting, and float bowl with acc. pump bypass jet. I have been very happy with the results. Others have tried the various aftermarket parts such as larger acc. pump wells, venturi plates, and so on, with generally good results. Let's see who else replies. You can get much better performance out of that carb. Good luck!