912 floods at idle

Thanks I'm going to reweigh the floats with a better scale. 

When(ever) you rebalance the carbs, don't forget to check the idle-mixture screws' positions!

I have had a similar problem with my 2006 912ULS with 560 TTSN. The old cork carb bowl gaskets (original equipment) were going bad and chunks were showing up in the carb bowls. Flew the airplane but upon landing, the same problems returned. The real culprit proved to be the carb floats (again, original with the airplane) that were decomposing with small black flecks coming off the floats and clogging the jets. Hope this helps.

Make sure the compensating tube between carbs does not have a microscopic crack in it which would allow it to suck air at low rpm where vibration is more than high rpm. Check also attaching hoses and one section where a small screw is inserted. 

There is a possibility you have an airleak causing engine to run too lean and running rough at low rpm. 

It could be many other things also like electronic ignition system.