My Solex is idling (actually more like barely stumbling) at about 600 rpm, after the motor is warmed up. I won't idle at all until I let the motor warm up for 5 minutes. I tried and bump up the idle air screw on the Solex, but unlike the photos in my Clymers, Chiltons, and my original 71 factory Opel manual, this Solex has a tube that is part of the carb casting that is about 1 and 1/2 inches long that juts out where the idle air screw should be. The screw is not visible at all, appears to be inside of this tube? Could this be a later model Solex from a 73 that cannot be bumped up? If I loosen (counterclockwise) the screw even a tad, it won't idle at all. I can only tighten it back (clockwise) to where it was idling originally, at 600 rpm, and it won't turn any more. Has anyone ever seen a Solex like this on a GT? The car is a 71 GT, but has held some "surprises" as I work on various parts of the car. (The trans turns out to be from a 73, for example. The new '71 back up light switch I bought cannot be installed, I just found out, because there's no place to put it in the tranny. The later models had different b/u light switch arrangement and wiring, from what I've gathered from this forum. Guess I'll just have to mickey mouse some wacky b/u switch arrangement to pass inspection. Any old Opel mechanics out there who know any tricks on bumping the idle speed up on this later model (I'm guessing that's what this thing is) GT Solex carb? It's got new plugs, wires, and it runs really smooth, excellent, actually, if I hold the pedal at about 900-1000 rpm. The carb doesn't leak, has been professionally rebuilt. It just idles too low.