I'm speaking of WR450f 2006 and newer. They do not have adjustable stock needles. There is a chance your bike has an aftermarket needle. I have experienced your symptoms tuning 2006-2009 bikes. The Dynojet needle and jet system is hard to get dialed in. We ran 150 main with the needle one down from the top. Sea level Balls Hot Summertime Florida. If you faise the needle more, the surge happens sooner in the RPM band. Your jetting is not far off, I'd try leaner main jet ant try diff positions.