Sounds like its definetly running too lean.It's either not getting enough fuel due to a problem with the carb(clogged pilot jet) or fuel delivery(pinched vent lines,plugged filter,dirty gas tank etc) or its getting too much air( bad crank seals or loose carb,air filter etc)..If it is just the choke it should run ok once the engine warms up.

 

I too, think its an air leak of some type. Like oldyeller said, if was the electric choke it would run OK once it got warmed up. The simple fact that you have to manually shut off the air tells me that it is getting to much air to begin with, atleast in comparison to the amount of gas it is getting. The other side of this same coin would be like itch was saying, a fuel delivery problem. Have you checked the vent lines on the carb yet?

 

You were absolutely right. We put a new top end kit on, but found a casting hole that caused a major air leak from one of the transfer ports to the outside fin area.