I understand this carb has an autochoke with a wax inside. Once warmed up by the coolant it relaxes the piston and slows the rpm down to a normal idle rate.
Now if the thermostat is faulty, i.e open then it will take much longer to warm up the coolant to melt the wax.
I want to eliminate that possibility first.
Also apparently there is an adjustment screw at the back to limit how much the auto choke opens.
I will experiment with this screw as the cold idle rpm is way to high until it heats up and settles to 750 ish.
I can see the piston open at cold and takes ages for the wax to melt and return the piston
https://forum.lowyat.net/topic/3404887/+2580