I've been experiencing erratic idling characteristics on my 1969 W115 200 Petrol for the last couple of days. It's not the ususal "rough" or "cycling" that plagues the older carbs of this type but rather, a "sometimes high" "sometimes normal" RPM kind of problem. I've had the car for some time now and this is the first time this has happened. Would it have anything to do with the "thing on top" that you put oil into? I'm clueless.