I recently bought a 1952 John Deere B gas burner that won't run smoothly. The carburetor has been rebuilt and I had it checked again yesterday and was told it is in great shape. When I try to smooth out the idle with the idle jet, it clears up for a while and then acts like it is starving. When I pull out the choke briefly it catches for a while. Fuel comes out the bottom drain on the carb. when I open it. At both idle and run it seems to be running rich from looking at the stack. It appears it's starving for either air or fuel--maybe both. Any suggestions would be most appreciated.