Just got in the door and read this message. Give me an hour or so and I'll pull the top off of one of my 46-IDA3-C carbs and compare the profile for fittment. I'm guessing the "fixture" will rest in the carb top plate (inverted) and aligns with some casting cavity for the vent hole drilling if needed.
It has been a while since I have been into these carbs but I never experienced any high temp - vapor/pressure build up in the 46's. Possibly only a 48-IDA issue??? I'll take a look - see.
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