dude... had the same thing recently.. I checked everything... I mean everything... carbs, reeds, jets, switched wires,etc..
found out I had a bad plug!!! Ive never had that happen to me in my life on any of my toys.. just not producing a great spark.. found it when I switched their sides left to right... bought a new one and ran perfect... go through a checklist first before you rebuild.. you might even find why it went bad in the first place (if the top end does need a rebuild)