Read through HDF techs about rejetting a CV carb and it has alot of good information in it. My own experience on it is to go with the Sportster needle and run it with the stock jet. The EPA doesnt care what is blowing out the exhaust while your riding down the road they're just looking at idle emissions. The only other mod I did was to up the slow jet. No drilling holes or cutting springs, they work just fine. Mines been running fine for almost 10 years. Two simple changes.