Steve,

I don't really know what you mean by choke!

The carb barrel should close all the way when the throttle trim is moved down. Sounds kind of like a linkage trim problem to me, although there maybe a problem at the carb that will not allow the barrel to fully close. Once you have the carb barrel opening and closing fully you should be able to set a good idle. This will allow you to taxi out and land at idle or just above, then trim down to shut the engine off once the flight is over.