Six pack secondary paper clip test?

There are two different ports on the ctr carb, off the main body is for the end carbs. The port from the metering block is dist vac. You say there is no vac for the end carbs, with the engine running, pull the hose and see if you feel any vac with opening and closing throttle.
There are actually 7 different springs, not positive, but brn is stock. Usually the tall yellow is what you want, there is a short yellow. I have run the purple and yellow.
The spring sets are available from Chicago Carburetor. You will need two sets. They each come with a chart of values for large and small cu in engines. Having gone through a couple sets of these, they may be due for an overhaul. Most of the gaskets are different, the ends are the same, the center is different, possibly someone has been in there and crossed something up. If you do them yourself, the air/idle adj screws on the end carbs will probably be stuck, soak them with blaster for a day or two . Will save you some grief from breaking them. If the carbs are full of a white looking substance, it's from alcohol gas, vinegar will dissolve it, but will also take the gold plating finish off. Sometimes you can't win! Those screws go back in 1/8th of a turn out.
Keep trying!