I have a YFZ450 that wont start. When you hold your hand over the intake you can feel it blowing, when you put your hand over the exhaust it sucks. So here is what I have done so far. I have checked the timing and rotated it 180 and checked the valve clearance and adjusted it. After I redo the timing and crank it by hand its fine it will suck through the intake and blow through the exhaust. But when I crank the bike it switches back to blowing through the intake after a few seconds of cranking. What am I missing?