I'm converting my '98 400 to a 426 and using my 400 carb. I'm running a Hot cams exhaust cam and a white bros E series. Foam filter in a stock YZ box. I usually run at about 1500-3000 feet elevation. I was thinking of starting out with stock 426 jetting, but the carbs must be different because the 426 has smaller stock jets. Does anyone know of a good baseline to start with?