1973 Mercedes Benz problem, please help!?

I'm about to purchase a 1973 Mercedes 280c! It runs like a monster! Sounds beautiful! The only thing thats wrong with it is it will not go into gear! It sputters and shuts off! i believe its because the owner adjusted a pin on the carburetor (a screw with a spring on it, finger tight thats adjustable) and it will not go into any gear besides park and neutral! Any help on how to readjust this pin, what pin it is, or even if ive got the wrong idea would be greatly appreciated! Thanks guys and gals!