300ex carb problems?

[craigdieselmac]

My dear 300ex now has a new problem. It will not run correctly unless it is choked all the time. If I un-choke it and try to goose it, it dies out on top end and comes back when it comes down a little. It acts normal as long as it is choked. I checked all the boots around the carb, cleaned the filter and nothing. I even took the carb off, cleaned it, and put it back on, nothing doing. I changed the spark plug in a moment of desperation.. nothing doing still. It seems to be rich when choked as it is blowing black exhaust when I goose it. If anyone has any ideas.. let me know!
Thanks
Jeff