Ignition setup recommendations

I just can’t understand it. If I leave off the foot brake it still cuts out, but just once. On the transbrake it’s 3 times very violently. On regular asphalt it doesn’t do it at all since the tires spin a bit. It’s obviously something that is effected by shock. I’ve chased every wire, disconnected my shift box, unhooked the tach, turned the rpm limiters all the way up, fattened and leaned the fuel. If it was fuel or ignition you’d think it would happen every time, and at more than just the starting line. Totally baffled.