I also had the same thing happen caused by a partially blocked main jet but you really should have done a leak down test before you tore it down just to verify if you had an air leak or not. Check your carbs over real good and post your jet sizes, did you notice any cracks in your intake on that side, was everything tight? If your jetted right on the edge of lean, a small air leak is all it takes.
This happened within 5 min of riding.