Just saw this on Reddit, looks like it might apply:

"Once I spent an entire weekend trouble-shooting an EX500 (twin cylinder Kawasaki) that would only run on one cylinder. The spark plugs, the float levels, the carb jets, the wiring harness, all connections, even checked the valve clearance and inspected all the valvegear.

Turns out an ant had crawled up a carb vent tube and wedged his tiny little body in just the right place in one little vent tube in one of the carbs. This mighty insect brought 600+ pounds of machine and man to a dead stop for an entire weekend. By weight, that would be like me stopping a cruise ship."