Car keeps cutting out!!!

[GRIFF55]

Hi all!! Bit of help needed please.
I used a 10x2 checkpoint at coventry regionals and my car ran fine(no overheating and temporarily stopping as it did the week b4). Its a trf 501x with too many holes in the body . Raced the car at ledbury this weekend, same gearing etc and it kept stopping 3.5/4 mins into race, then would go again and so on.
I had it geared at 16/96, stormforce 4200 cells, anyone got suggestions, is the speedo limited, undergeared, overgeared, as its starting to me!!!
Thanks all.