I'm having the same issue with mine, both cylinders fire up then 2-3 seconds afterward the left cylinder stops firing. I cleaned the carbs, reeds were perfect, changed plugs, swapped wires and still left cylinder is failing. I guess a compression test is next. Wish me luck. I'll report back once the test is done (crossing fingers). My bike is a 2006, ported, milled head, VF3's, T6's, stock carbs, +4 timing, bored .20 over.