This one has me baffled. I'm sorta a rookie when it comes to jetting although I've done it many times before. All I did was rejet my 2007 YZ450F hich is totally stock (pipe and everything). I live at 360 ft. elevation (sea level). I went up one on the pilot to a 48 and up one on the main to a 162. went to start it and using the choke it started up after a few kicks. Let it idle for about a minute then tried to turn off the choke and it died. Went to restart and nothing!!!!!!! Any suggestions before I return to the stock jetting??? I haven't messed with the fuel screw yet. Was thinking of turning it to about 1 turn out to start and try again. Is it possible I tightened the jet too much?