I had a problem with my DA50 almost identical to the problem you are having. In addition to what you descibe, mine also would not prime unless spun over with an electric starter. At idle it shook like crazy and was way down on top end. When I called DA and described the problem to them I was promptly informed that I was lying. Anyway, after a long argument they agreed to send me a new carb. Put the new carb on and it runs just fine now.