On the starboard side of the carb is the choke mechanism. That old style uses a rod that goes down to the little metal housing on the intake manifold. Inside is a coiled bi-metal spring. When cold, it shuts the choke flap on the carb. As it warms up, it opens the choke. There is a fast idle screw located down low below the choke linkage and it determines how fast the the idle is when the choke is engaged. About 1500 rpm is right. There are two things you can do. One is to unscrew that fast idle screw so the engine barely speeds up at all. The other thing you can do is to fully open the choke and then use a tie wrap or a bit of wire or something to keep it open. That will disable the choke. The whole idea of a choke is to help the engine run better while it is cold. When you first press the gas pedal the accelerator pump squirts gas into the carb. The choke closes to force more gas from the fuel feed circuit. The fast idle screw opens the throttle so it runs faster. But as soon as the engine fires, the choke pull-off [that vacuum can on the front of the carb] cracks the choke flap open a small amount to give more air. Otherwise if the flap stayed closed the engine would over-choke and die. As the engine warms up the coiled spring on the manifold warms and opens the choke flap until it is totally open. The fast idle screw drops down the steps and lets the engine slow down. Once at operating temperature and the flap is completely open then the curb idle screw on the port side determines the idle speed. Since you are running it on a stand I would disable the choke so it just runs slowly. Once it is in the car again I can walk you through getting it all set up correctly.