This past weekend I changed my jetting for the first time. My 426 had the stock jetting which wasn't that much off but did need some fine tuning. I went with the recommendations I got off of the website http://www.strokerspeed.com. They recommended going to 48 pilot and 165 main, with the fuel screw 2 turns out. I'm in NM at about 4000 feet and they said these specs were good to about 5000 feet. Anyway just letting you know that these specs seem to be spot on after testing.