Sounds like the boys have it covered
Does sound like an idle gap / too rich problem. Either the idle gap is too small and the motor is simply stalling, or it's too rich on the bottom and it's loading up after a full throttle burst and choking itself. If it's too lean on top it would normally die as you accelerate away, say around half throttle. Just crank the idle up a little and see what happens. Maybe try a hotter plug too.
Matt, that's a good idea about the servo settings too. I run ACE 15 kg servo's for steering and throttle/brake (mainly due to the speed of operation on the throttle/brake). I never have the throttle /brake servo EPA set at any more than 70%. I then set the adjustable brake exponential on my Spektrum to 70% as well, and then set up my brake linkages from there. This setting provides ample stopping power and saves wear and tear on the servo and the linkages. If I do need more stopping power or get a bit of brake fade, I have another 30% of travel I can dial in on the run, and still not be pushing the servo past 70% of its max travel.