After putting 30 miles on bike I changed stock 150 main jet to a 160 MJ. I only did the main jet at that time because the dealer didn't have pilot or starter jets in stock. What I noticed after MJ was changed was the bike ran better but after shutting bike off I would get a pop from exhaust 80% of the time.Another thing I noticed was when I grabbed a fist full of throttle I'd get a hesitation before she would get up and go. I chalk that up to being a lean pilot jet. Saturday I pulled the carb off and changed the stock pilot jet ( not quit sure what was in there ) to a #48 Like 70% of what TT'ers with WR450's are using and also changed starter jet to a #72. After these changes I found hesitation is still there but not quite as bad. Pop is now heard on engine starts and not engine stops. Not a full backfire just a pop. Bike will start on a 50-60 degree day without choke but will stall after 5-10 seconds. I also can restart hot bike without hot start lever but it will fire alittle faster using it( still popping on restart). It seems to me it's a fuel screw adjustment (have to go leaner on fuel screw) but I'm new to all this jetting stuff. I did order the ZIP-TY fuel scew but have not recieved it yet. Seems alot of TT'ers are waiting for theirs also.