This problem has just started in the last two months. On the first start of the day, the engine starts normally, but will not transition to high throttle. When the throttle is advanced, even partially, it sags and dies unless the throttle is retarded back to idle. After running at idle for 30 to 45 seconds, thransitions are normal and will continue to be OK for the remainder of the day. Any ideas?

when the low end is set correctly all DA engines will not transition when the engine is cold. If you richen up to run good cold it will be to fat after it is warm. Sounds like to me you have it set correct. If you put the choke on a servo and use a variable rate on the transmitter you can give it about half choke and it will transittion fine cold.

FWB

I'd agree with FWB, a properly tuned DA, just about any DA will react like that. If the engine has less than 5 gallons through it you might want to consider richening it up just a touch

You can easily check to make sure it's tuned correctly, pull the plugs after a flight and look at their color a medium to light color tan is good, dark tan is just a bit rich

Yep I agree too. Just let it idle for 30 seconds and do nothing while it warms up. Once it's warm it will transition. Or use the partial choke, either way works great.