On Tuesday, March 31, 2020 at 9:08:25 AM UTC+11, SoaringXCellence wrote:
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."

Thanks for the suggestions. I have bought new spark plugs (NGK B7HS) & will fit them for the next test flight. We tested the existing plugs (I won't call them old - they'd only run for 15') hoping we'd find one faulty - covering all possibilities. Rgds, Bill