Apart from the possibility of one jet drive being stiffer than the other thus allowing one to start rotating easier than the other, there is also the possibility of slight differences between the motors and the responses of the ESCs. Try substituting, swap the ESC/motor combinations over and note if the problem stays where it is or moves, then do the same with the motor/jet drives. You need to know which bit the problem is coming from before you can start to cure it.