idle too high, makes undriveable

Most definitely check for vacuum leaks. Just had a similar situation, but I'm running a race carb with no choke. First start up we idled it up to 2500 rpm which didn't take much adjustment. After break in, I tried totadjust the idle to set point. It wouldn't go below 1200 and that's when I heard what I thought was just air going into the carb. I got to searching and found a 3/8 Barb I had overlooked that was open. I put my finger over it and the idle dropped down to 3 - 400 before it died.