912 floods at idle

Well you could weigh floats both sides without taking carbs off. My rotax I noticed fuel coming out of vent tube at idle and after shut down but no ruff running. One set of float was 12 grams the other 6.3 grams. So I replaced both sets very easy and no more fuel coming out of vent tube that had the 12 grams one. Well, 150 dollars a set. 

NOW the choke does not operate like normal chokes on other carburetors. Very easy to just look and make sure both sides disengaged. On 912 choke only works when throttle at idle cutoff. Start with it on, turn off and start engine again with a little throttle brakes on.

Auto gas very unstable and if left in for a while causes issues. I burn 100LL aviation fuel in mine. The guy before me used none alcohol auto gas. Even if you use auto gas with stable in it, I recommend before letting engine sit a while put 100LL aviation fuel as last tank before winter hibernation. 100LL you can leave for years it will cause no issues and engine will start. You just have to drain and make sure n water in tank. 

Are the carbs shaking? Is this a Kitfox 4 or an aicraft with the intake manifolds are reversed?

this causes the carbs to shake and the fuel to froth.

Well the floats are 3 grams each and the chokes are completely closed. 

Floats are 3 grams each and chokes are all the way off?

"It loads up so bad the idle will drop down to 1100 rpms."

This sounds like carbs. Something in the carbs, fuel feed and or pressure seems off or throttle cable issue? If you are using gauges to sync the carbs vs an electronic device you should be able to see what's going on when the gauges are hooked up and the plane rpm dives down.

If the floats are good and the chokes closed then I would make sure the float pins that the floats ride up and down on are straight and no float is getting hung up on the bowl sidewall. Then I would check the float brass armeture for the proper height. 10.5mm from the bowl edge to the top of the brass float armeture. If you're only off .5mm that shouldn't be your issue. Last, but not least could it be something in the needle valve opening? Possibly. Not real common.

If you have a carb flooding and running rough not sure how the carbs would sync up. 2K rpm should be running smooth.