quote:The vacuum line that you see running to the center carb is for the automatic choke. Picture 19 (floor pan) bothered me too. Looks kind of beat up. I still think this is a nice car. The vacuum secondary carb linkage set-up used a mechanical vacuum switch attached to the center carb, a vacuum diaphram attached to the front carb, a vacuum reservior tank and a thermal vacuum switch screwed into the coolant passage in the intake manifold. When the center carb approached WOT, it opened the vacuum switch which allowed vacuum from the vacuum tank to be fed to the vacuum diaphram. The vacuum diaphram would pull and open the front carb. The rear carb would open simultaneously via a mechanical rod attached between the front and rear butterflies. The thermal vacuum switch was placed in between the vacuum tank and the vacuum switch which prevented the front and rear carbs from operating when the engine was cold. I've only seen a few vacuum secondary set-ups (I have one on the shelf), but I've never seen them in operation. Lots of vacuum secondary set-ups got switched over to mechanical secondaries because the rubber and other parts would would wear out and deteriorate and replacements are impossible to find, AFAIK.
Originally posted by Pablo: paulo57509 - interesting observation (you obviously know your Pontiac engines) - but when I look at picture 17, it looks like vacuum lines to the carbs. Just trying to learn, thanks. Why does picture 19 bother me?