Sounds to me like the guys at the field dont know what they are doing. You need to tinker with the mixture. there is a little screw that you need to adjust. Its going to take some time to get it right as its usually set at the factory, and if they messed with it then its messed up. Try this let it run and then idle it down if it quits then turn the screw just a little maybe a 1/4 turn. The run it again. Sounds to me like its running lean, to much air and not enough fuel. Its just going to take some time to get it right.

Alan