try trimming the radio for abit higher idling.Can't really say what's the problem.Have you done this checklist?

1. Does the carb close all the way when you brake? [ re adjust the throttle servo or the idling screw on the carb ]

2. Is your motor running too rich? [ Motor floods over and the glow plug fouls thus the motor dies....lean it]

tell us more... . Is the rpm right?.Is the throttle servo stripped?