It sounds to me the float level is too high. It,s normal for the engine to richen up with the choke out but if it,s overdoimg it the float may be setting the fuel level too high. Try setting the timing up a little. With a roch. B carb the vacuum advance line goes to na fitting on the right side near the idle screw. Like Hot Rod says there should be no advance at idle. A poor mans exhaust annilizer is if it hesatates when cold with the choke in & runs good after warmup the mixture is about right. I worked on step vans for 35 years. I know what positions you have to get your body in to work on them.
