Yep, blue/white smoke is a very rich mixture. But am confused why it only happens when the engine is at operating temp. Seems to me if the fault is from overflow (stuck needle or float) it would do it all the time.

Am in agreement the possible causes may be the needle or float. The needle comes with the kit, but the float must be ordered separately. Time to take that baby off and see what is what. You can just inspect the float/needle with out taking the Solex off. Unscrew the 4 nuts and take the 8 cover screws out. These are different lengths so be sure to lay them out in a pattern. Take the cover off and see what is what. When replacing the cover do not over tighten the screws as they will strip out the body threads. Also, the bolts Must be torqued down. The torque spec is 10 Nm with a new flange and 8 Nm using the old flange. I torque by even numbers: 2,4,6,....Nm until you get to the specified spec.. Takes a little more time, but is the proper way to torque.

The float is subject to pressure spillage if it has too much pressure coming in. It could be possible the fuel return/pressure valve is not working as well and is often overlooked.