I have one additional suggestion.
Check to see that the idle stop are correctly adjusted. Normally this is set on the front carb only. There is an adjuster with a lock nut and you may need to pry the cap off the top to turn the adjuster. Once off cold idle, this is what controls idle speed.
You may have float housing vent valves. These need to be adjusted to open the correct amount when the actuating levers are against the idle stops.
You may need to pry the cap off the top of the carb(s) to adjust the idle stop.
I would not give up on your carbs. They fact that you have a good cold start and warm up without backfire means that they are in basically good shape.
The key to keeping them that way is to make sure that the heat risers are not sticking in the open position. This is what causes the warping. MB sells a rebuild kit for the risers. If yours are sticking in the open position, turn them manually so they stick closed.
I have spare parts if you need them. Good luck!
Falls Church VA
'66 200, '66 230SL, '96 SL500. Sold: '81 380SL, '86 300E, '72 250C, '95 C220, 3 '84 280SL's '90 420SEL, '72 280SE, '73 280C, '78 280SE, '70 280SL, '77 450SL, '85 380SL, '87 560SL, '85 380SL, '72 350SL, '96 S500 Coupe