I'm having the EXACT same problem. I checked and double and triple checked everything. My problem was the reeds. They are very sensitive. Mine were not sitting flush and the gap was so little (less than the width of a razor blade) between the reeds and the cage that I didn't notice it in the 10 or so times I had it apart. Tap on the reed and see if it makes a clicking noise when it hits the cage. If it does, they may be warped. If that's the case, get new reeds, new plug and it should kick right over. If not the reeds, a carb/jetting issue maybe?