Searched, found a description that matches my friend's inquiery. Can anyone fill in more of the gaps? "I saw something interesting/weird at the junkyard yesterday. Since I got my carb rebuilt by a performance shop, I've been on the look out for an old Rochester Quadra Jet as that is what he recommended as the best off road carb. Anyway, apparently this is a highly sought after item at the local Pull A Part yard as they seem to be missing off of all the cars that originally came with them. Yesterday, I saw a carb just laying on the intake and the intake had the tell tale small primary holes/large secondary holes. I thought I had really lucked out but when I picked up the carb, it really was strange. It had butterfly valves and the normal hardware on the primary side, but nothing on the secondary side. No butterfly valves, shaft, linkage, etc, absolutely nothing. In fact, on top of the carb, the secondary side had a cover plate with the logo Rochester Dual Jet. Obviously this was some sort of weird configuration, but I'd never heard of it before. Can anyone tell me what GM was thinking with this configuration? Was it some sort of low emissions version? Higher mileage? It looked like it could have been turned into a normal one if it was machined for the shaft and the rest of the parts were added."