hmm, this is a tricky one, I would do a few things check to make sure your floats aren’t sticking, this could cause a “too much fuel” problem. I would also do a carb sync to make sure they are all running consistently. check the plugs to see how they look, are they gapped properly? are all 3 cylinders firing? check to see if all three header tubes are getting warm. are your vacuum caps in good shape? plugged? if you get it running good again and can take it on another ride, try riding with the gas cap popped (make sure the tank isn’t super full so you don’t get spillage out the top) and see if it dies again at that 24km mark. I experienced something similar to the dying while riding problem, the gas cap on my bike wasn’t venting properly/quick enough for whatever reason and it would actually prevent the gas from flowing down into the carbs and would cause it to starve for fuel, it would then eventually equalize pressure and flow down and was able to start again.