Check the choke assembly on the carb. The choke plate should be blocking off air flow when the engine is cold. On the stock carb, the plate should be in the horizontal position when cold. As the motor warms up, the plate should gradually open, allowing more air in, and the idle speed will begin to slow down. When fully warm, the choke plate should be vertical.
If your carb has an electric choke, check that the choke is closed before starting the engine when it's cold.
the choke should be closed (horizontal) when the motor is cold, and should be open when the motor is hot (vertical).
If it's stuck at a 45* angle, sounds like it might be your problem.
I think the position of the plate when the motor is off depends on how warmed up it was when it was last shut off.
Is your choke electric or manual? If it's electric, try moving the plate with the ignition switched on.