carb sync tool works well to sync carbs at idle together, its the most accurate way. I only use the tool to sync them at idle part throttle you can basically eye it.
if its staying idled up like that for 1-3 seconds, and there are no air leaks, reeds are good and cable is fine, run your air fuel screw all the way in, then put it at a half turn out, see if that helps, stock pilot? 25